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4V 



Harper's Practical Books for Boys 

A SERIES OF NEW HANDY-BOOKS 
FOR AMERICAN BOYS 

Each Crown 8vo, -with many Illustrations. 



HARPER'S OUTDOOR BOOK FOR BOYS 

By Joseph H. Adams. With Additional Contribu- 
tions by Kirk Munroe.Tappan Adney, Capt. How- 
ard Patterson, L. M. Yale, and others. Cloth, $ 1 .75. 
II 
HARPER'S ELECTRICITY BOOK FOR BOYS 
Written and Illustrated by Joseph H. Adams. With 
a Dictionary of Electrical Terms. Cloth, $1.75. 

IN PRESS 
III 

HARPER'S HOW TO UNDERSTAND ELEC- 
TRICAL WORK 

A Simple Explanation of Electric Light, Heat, 
Power, and Traction in Daily Life. By Joseph 
B. Baker, Technical Editor, U. S. Geological Sur- 
vey, formerly of the General Electric Company. 

IV 
HARPER'S INDOOR BOOK FOR BOYS 

By Joseph H. Adams and others. Cloth, $1.75. 
V 
HAxRPER'S MACHINERY BOOK FOR BOYS 

The Boy's Own Book of Engines and Machinery. 
Cloth, $1.75. 



HARPER & BROTHERS, PUBLISHERS, NEW YORK 



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ti S 




Copyright, 1907, by Joseph H. Adams, N. Y. 
THOMAS A. EDISON DICTATING TO HIS GRAPHOPHONE 



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HARPER'S 
ELECTRICITY BOOK 

FOR BOYS 



WRITTEN AND ILLUSTRATED BY 

JOSEPH H. ADAMS 

author of '^ 
" harper's outdoor book for boys " 



WITH AN EXPLANATION OF ELECTRIC LIGHT, HEAT 
POWER, AND TRACTION BY JOSEPH B. BAKER 
TECHNICAL EDITOR, U. S. GEOLOGICAL SURVEY 

AND 

A DICTIONARY OF ELECTRICAL TERMS 




HARPER & BROTHERS PUBLISHERS 

NEW YORK AND LONDON 
MCMVII 



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LIBRARY of CONGRESS 
TwoCeoy R^xfttved 
NOV 14 1907 

_ Copyricht Entry 
OUSSA KXc. No. 

I g / fe7<2?J 

COPY B. 



Copyright, 1907, by Harper & Brothers. 

All rights reserved. 
Published November, 1907. 



CONTENTS 



PAGE 

INTRODUCTION xi 

Part I 

CHAPTER I.— SOME GENERAL EXPLANATIONS .... 3 

An Invisible World-power— ^Generating Electricity — 
What a Boy Can Do — Inexpensive Tools — Some Prac- 
tical Advice ; 

CHAPTER II.— CELLS AND BATTERIES 12 

Simple and Inexpensive Cells — How to Make Cells and 
Batteries — A Plunge-battery — A Storage-battery — 
Dry-cells and Batteries 

CHAPTER III.— PUSH-BUTTONS AND SWITCHES .... 33 
How to Make Push-buttons — Switches and Cut-outs — 
Table-jack Switches — -Binding-posts and Connectors — 
Lightning-arresters and Fuse-blocks — Some Practical 
Precautions 

CHAPTER IV.— MAGNETS AND INDUCTION-COILS ... 54 
Simple and Horseshoe Magnets — Induction-coils — An 
Electric Buzzer — Electric Bells — A Large Induction- 
coil — Circuit-interrupters 

CHAPTER v.— ANNUNCIATORS AND BELLS ...... 78 

A Drum-sounder — A Simple Annunciator — A Double 
Electric Bell — An Electric Horn — How to Make a 
Burglar-alarm — Electric Call-signals — Clock-alarms 
— A Dining-table Call 

vii 



CONTENTS 



PAGE 

CHAPTER VI.— CURRENT-DETECTORS AND GALVANOM- 
ETERS 102 

How TO Make Detectors — An Astatic Current-detector 
— An Astatic Galvanometer — A Tangent Galvanometer 



Part II 

CHAPTER VII.— ELECTRICAL RESISTANCE 125 

Governing the Electric Current — Ohm's Law — Re- 
sistance - COILS AND Rheostats — How to Make Sim- 
ple Apparatus — Liquid Resistance — Importance of 
Switches — Uses of a House-current — Running a Sew- 
ing-machine, Fan, or Toys — An Easy Method for a 
Boy's Use 

CHAPTER VIIL— THE TELEPHONE . 156 

Vibratory Waves — A Bladder Telephone — A Single 
(Receiver) Line — Plan of Installation — A Double- 
pole Receiver — The Transmitter — Another Form of 
Transmitter — The Wiring System^ — A Telephone In- 
duction-coil — • An Installation Plan — A Portable 
Apparatus 

CHAPTER IX.— LINE AND WIRELESS TELEGRAPHS . . 190 
A Ground Telegraph — How to Talk from House to 
House — The Morse Telegraph Code — A Story of Edison 
— How Detectives Used the Code — Wireless Teleg- 
raphy — Its True Character — How a Boy Can Make 
a Practical Apparatus — Receiving and Sending Poles 
— Induction-coils, Batteries, Coherers and De-coher- 
ers, etc. — Working Plans in Detail — Aerograms Across 
the Atlantic and, perhaps, Around the World 

CHAPTER X.— DYNAMOS AND MOTORS ' . 229 

Dependence of Modern Electricity upon the Dynamo 
■—A Field of Force Cutting another Field of Force—' 

viii 



CONTENTS 



Varieties of Dynamos — Simpler Form^ of Generators 
AND Motors — How to Make a Uni-direction Current 
Machine — Permanent Magnet, Armature, Shafts, 
Wheels, etc. — A Small Dynamo — Machines to Light 
Lamps, Run Motors, etc. — A Split-ring Dynamo — A 
Small Motor — The Flat-bed Motor— Motors of Other 
Types 

CHAPTER XI.— GALVANISM AND ELECTRO-PLATING . . 266 

A Fascinating Use of Electricity — A Simple Electro- 
plating Outfit — The Sulphate of Copper Bath — How 
TO Make the Tank and Other Apparatus — A Variety of 
Beautiful and Useful Results — Explanations of Vari- 
ous Batteries — The Cleansing Process — The Plating- 
bath— Silver-plating — Gold- plating — Nickel- plat- 
ing — • Finishing — Electrotyping — Practical Details 
of Interesting Work 

CHAPTER XIL— MISCELLANEOUS APPARATUS 294 

Making a Rotary Glass-cutter — To Smooth Glass 
Edges — Cutting Holes in Glass — Anti-hum Device for 
Metallic Lines — A Reel-car for Wire— Insulators — • 
Joints and Splices — "Grounds" — -The Edison Roach- 
killer — An Electric Mouse-killer 

CHAPTER XIII.— FRICTIONAL ELECTRICITY 312 

Its Nature — Limited Uses — Simplicity of Apparatus — 
A "WiMSHURST Influence Machine" — -Materials Re- 
quired — -Glass, Tin -foil, Spindles, Uprights, Wheels, 
ETC. — -A Large Leyden-jar — Apparatus for Interesting 
Experiments — Necessity of Caution 

CHAPTER XIV.— FORMULA 327 

Acid-proof Cements — Hard Cement — Soft Cement — 
Very Hard Cement— Clark's Compound — Battery Fluid 
— Glass Rubbing — Acetic Glue — Insulators — Non-con- 
ductors — Insulating Varnish — Battery Wax 

ix 



CONTENTS 



PAGE 



CHAPTER XV.— ELECTRIC LIGHT, HEAT AND POWER . . 334 
(By Joseph B. Baker) 

The Work of the Dynamo — -The Electric Light — Uses 
OF the Arc-light — Incandescent and Other Lamps — 
Electric Heat — Electric Furnaces — Welding Metals 
— Electric Car-heaters — Household Uses — Electric 
Power — Power from Water-wheels — Transformers — 
Rotary Converters — Oil-switches — Electric Traction 
— ^The Trolley-car — ^The Continuous-current Motor — 
The Controller — Electric Locomotives — Other Forms 
of Electric Traction 

A DICTIONARY OF ELECTRICAL TERMS 359 



INTRODUCTION 

IF a handy-book of electricity like this had fallen into 
the hands of Thomas A. Edison when he was a newsboy 
on the Grand Trunk Railway, or when he was a telegraph 
operator, he would have devoured it with the utmost eager- 
ness. To be sure, at that time, in the early sixties, all that 
we knew of electricity and its applications could have been 
told in a very brief compass. It was an almost unknown 
field, and the crude form of the telegraph then in use 
represented its most important application. There were 
no electric lights; there was no telephone or phonograph; 
there were no electric motors. Telegraphing, itself, was a 
slow and difficult process. All the conditions were as far 
removed as possible from the broad field of applied elec- 
tricity indicated in this book. 

But this does not mean that we have now accomplished 
all that there is to be done. On the contrary, the next half- 
century will be full of wonderful advances. This makes it 
more than ever essential that we should become acquainted 
with the principles and present conditions of a science which 
is being applied more and more closely to the work of every- 
day life. It is necessary to know this from the inside, 
not simply from general descriptions. Theory is all very 
well, but there is nothing like mastering principles, and 
then applying them and working out results for one's self. 

xi 



INTRODUCTION 



Any active and intelligent boy with an inquiring mind 
will find a new world opened to him in the satisfaction of 
making electrical devices for himself according to the sug- 
gestions given in this book. This will show him the reasons 
for things in concrete form, will familiarize him with prin- 
ciples, and will develop his mechanical ingenuity. He may 
be laying the foundation for inventions of his own or for 
professional success in some of the many fields which elec- 
tricity now offers. Work of this kind brings out what is in 
one, and there is no satisfaction greater than that of winning 
success by one's own efforts. 

The boy who makes a push-button for his ow^n home, or 
builds his own telephone line or wireless telegraph plant, or 
by his own ingenuity makes electricity run his mother's 
sewing-machine and do other home work, has learned ap- 
plications of theory which he will never forget. The new 
world which he will enter is a modern fairyland of science, 
for in the use of electricity he has added to himself the 
control of a powerful genie, a willing and most useful ser- 
vant, w^ho will do his errands or provide new pla3rthings, 
who will give him manual training and a vast increase 
in general knowledge. The contents of this book, rang- 
ing from the preparation of simple cells to the making of 
dynamos and motors, and the delightful possibilities of 
electro-plating, shows the richness of the field which is made 
accessible by Mr. Adams' practical explanations, his care- 
fully tested working plans, and his numerous and admirable 
drawings — all of which have been made for this book. 

It is in keeping with the practical character of the Elec- 
tricity Book that pains are taken throughout to show the 

xii 



INTRODUCTION 



simplest and most inexpensive way of choosing materials 
and securing results. The actual working out of these di- 
rections can be done at very small expense. Furthermore, 
there need be no concern whatever as to possible danger if 
the book is read with reasonable intelligence. Mr. Adams 
has taken pains to place danger-signals wherever special 
precautions are advisable, and, as a father of boys who are 
constantly working with electricity in his laboratory, he may 
be relied upon as a safe and sure counsellor and guide. 

While this book shows boys what they can do themselves, 
its scope has been enlarged by Mr. Baker's chapter explain- 
ing briefly the working of electricity all about us, in light 
and heat, in the trolley-car, and other daily applications. 
In addition, Mr. Adams has prepared a Dictionary of Elec- 
trical Terms, and these brief definitions will be found pecul- 
iarly helpful in the first reading of the book. It is believed 
that there is no book in this particular field comparable to 
Harper's Electricity Book in its comprehensiveness, prac- 
tical character, and the number and usefulness of its il- 
lustrations. It follows the successful Out -door Book for 
Boys in Harper's series of Practical Books for Boys, and 
it will be followed by How to Understand Electrical Work, 
a book, not of instructions in making electrical apparatus, 
but of explanations of the commercial uses of electricity all 
about us. 



Part I 



ELECTRICITY BOOK FOR BOYS 

Qiaptcr I 

SOME GENERAL EXPLANATIONS 

WE are living in the age of electricity, just as our fathers 
lived in the age of steam. Electricity is the world- 
power, the most powerful and terrible of nature's hidden 
forces. Yet, when man has learned how to harness its fiery 
energies, electricity becomes the most docile and useful 
of his servants. Unquestionably, electricity is to-day the 
most fascinating and the most profitable field for the in- 
vestigator and the inventor. The best brains of the country 
are at work upon its problems. New discoveries are con- 
stantly being recorded, and no labor is thought too great if 
it but add its mite to the sum total of our knowledge. And 
yet, ridiculous as the statement may seem, we do not know 
what electricity is. We only know certain of its manifesta- 
tions — what it can do. All we can say is that it does our 
bidding ; it propels our trains, lights our houses and streets, 
warms us, cooks for us, and performs a thousand and one 
other tasks at the turn of a button or at the thrust of a 
switch. But what it is, we do not know. Electricity has 

3 



ELECTRICITY BOOK FOR BOYS 



no weight, no bulk, no color. No one has seen it ; it cannot 
be classified, nor analyzed, nor resolved into its ultimate 
elements by any known process of science. We must con- 
tent ourselves with describing it as one manifestation of the 
energy which fills the universe and appears in a variety of 
forms — such as heat, light, magnetism, chemical afifinity, and 
mechanical motion. In all probability it is one of those 
phenomena of nature that are destined to remain forever 
secret. Thus it stands in line with gravitation, magnetism, 
the active principle of radium, and the perpetual motion of 
the solar system. 

Electricity was known to the early Greeks; indeed, it 
derives its name from the Greek word for amber (electron). 
For many centuries amber was credited with certain special 
or magical powers. When it was rubbed with a flannel 
cloth, "the hidden spirit" came out and laid hold of small 
detached objects, such as bits of paper, thread, chips, or 
pith-balls. No one could explain this phenomenon. It 
was looked upon with superstitious awe and the amber itself 
was regarded as possessing the special attributes of divinity. 
But as time went on, it was discovered that in various other 
substances this mysterious attractive power could be ex- 
cited, at will, through the agency of friction. Rubbing a 
piece of glass rod with silk or leather generated an ''elec- 
tricity ' ' identical with that of the amber ; or the same result 
could be obtained by exciting hard rubber with catskin. 
The conclusion followed that electricity was not a property 
of the special materials employed to generate it, but that 
it came from without, from that great reservoir of energy, 
the atmosphere. Then came Franklin with his experiment 

4 



SOME GENERAL EXPLANATIONS 

of the kite, and the invention of the Leyden-jar and the 
chemical production of the electric fluid by means of 
batteries. It was shown that the properties of the new 
and strange force were the same, whether it was pro- 
duced by the static (frictional) process or by the galvanic 
(chemical) method. Electrical science as a science, had 
begun. 

And yet, for many years, electricity was hardly more than 
a scientific toy. It was not supposed to possess any prac- 
tical usefulness. The entertaining experiments with the 
static machine and the Leyden-jar (chapter xiii.) were con- 
fined to the laboratory and the lecture hall. Electricity 
was an amusing display of unknown energy, but no one ever 
dreamed that it could ever be made to serve the practical 
ends of life. It was not until about 1850 that electrical 
science became anything more than a name. The galvanic 
and voltaic batteries (chapter ii.) opened the way for ''cur- 
rent" electricity, which flowed continuously, instead of 
jumping and disappearing like the spark from a Leyden-jar. 
When the continuous current became an established fact, 
the telegraph and telephone headed the line of a long series 
of developments. Finally, the generation of electricity in 
greater volume, and cheaply, made possible the application 
of its power for heating, light, traction, and the other forms 
of activity in which it now does so large a share of the 
world's work. 

How electricity works is a question often asked, but not 
easily answered. There are certain so-called laws, but we 
shall best arrive at a conclusion by simply stating a few 
of the facts that have been established through the ob- 

5 



ELECTRICITY BOOK FOR BOYS 

servation and investigation of scientists and electrical en- 
gineers.^ 

For example, electricity is always alert, ready to move, 
and continually on the lookout for a chance to obtain its 
freedom. It will never go the longest way round if there is 
a short cut; and it will heat, light, or fuse anything in its 
path that is too weak to carry or resist it. For this reason, 
it must be generated in small volume — that is, just sufficient 
to do the work required of it. If produced in larger volume, 
it must be held in check by resistance, and only so much 
allowed to escape as may be needed for the specified work. 
Again, when electricity is generated this must be done in 
one of two ways — by friction or chemically. But in both 
processes there must be air surrounding the generators, and 
the fluid must be of a nature through which oxygen and 
hydrogen can circulate freely. Water fluids are suitable for 
this purpose, but oils cannot be used, as they contain hydro- 
carbon in large quantities and are non-conductors. 

Batteries are chemical generators, dynamos are magneto- 
electric, and static machines are frictional. Now the theory 
is that electricity is drawn from the ether and, in its nor- 
mal state, is quiet. If it be disturbed and collected by 
mechanical or chemical means, it is always on the alert to 
escape and again take its place in the atmosphere. As its 
volume is increased, so its energy to get away is multiplied, 
and this energy may be transformed, at will, into power, 
heat, or light. To express the idea in the simplest language, 

* Explanations of any technical names or phrases used in the text will 
be found in the simple dictionary of electrical terms which appears as an 
appendix. 

6 



SOME GENERAL EXPLANATIONS 

it wants to go home, and in its effort to do so it expresses itself 
in the form of stored-up power, precisely like water behind 
a dam. It is for man's cunning brain to devise all sorts of 
tasks that this power must perform before it can gain its 
release. It can't go home until its work is done. 

Nearly every boy has experimented, at one time or an- 
other, with electricity and electrical apparatus, and whether 
it was with some of the simple frictional or galvanic toys, or 
with the more complicated induction-coils and motors, he has 
undoubtedly found it a most interesting amusement and an 
ever new and widening field for study. Then again, many 
boys would like to know something about simple electrical 
apparatus and how to make and use it. But his school- 
books relating to the general subject of electricity are 
hardly definite enough to serve as a practical manual. And 
yet there are many things in the way of electrical machinery 
and equipment that a boy can easily construct and use. In 
this book it is my purpose to show him just what can be done 
with the aid of the tools that are usually in his possession. 
While some things may have to be purchased from an elec- 
trical supply -house or other sources, there is still much 
material to be found about the house that may be put to 
good use by the amateur electrician. 

It is not possible or desirable to describe every variety of 
electrical equipment. We must confine ourselves to appa- 
ratus which can be readily understood and operated. The 
"practical" idea is the one to be borne in mind. This book 
shows a boy how to use his brains and the simple tools and 
material that may be at his command. Care and thought 
in the construction of the apparatus are the important 

7 



ELECTRICITY BOOK FOR BOYS 

qualifications for success. The instructions are given in the 
clearest possible language; the diagrams and drawings are 
intelligible to any one who will take the trouble to study 
them. If your finished apparatus does not work properly, 
read the description again and see if you have not made some 
error. A misplaced or broken wire, a wrong connection, or 
a short circuit will mean all the difference between success 
and failure. 

Save in one short chapter, static or frictional electricity 
(see Appendix) is not considered ; for outside of laboratory 
experimenting and electro-medical apparatus, frictional 
electricity is but a toy — interesting and useful when gen- 
erated in small volume, but very dangerous and difficult of 
control when in great volume. For example, the bolt of 
lightning is but the many times multiplied spark stored in 
the Leyden-jar by the static machine. For all practical 
purposes, galvanic electricity, in its various phases of direct 
and alternating current, meets the requirements of man. 
With the improved apparatus and the rapid advancement 
along the line of invention, electricity is as easily controlled 
to-day as steam — in fact, its economical use is even more 
fully under control and its adaptability more practical. 

In the following pages there are probably illustrations 
and descriptions of many things that will seem strange to 
the boy who has not heard of them; but if a book were 
written each year on the subject of electricity, every new 
one would include principles and facts not known before. 
The field of electrical research is so broad and so many are 
working in it that new discoveries are being made con- 
tinually. 

8 



SOME GENERAL EXPLANATIONS 

To those familiar with the appHcation of electricity, it is 
clearly evident that, as yet, we are only beginning to deal 
with this unknown force. For generations to come, develop- 
ments will take place and invention follow invention until 
electricity assumes its rightful place as the motive force of 
the world. To the boy interested in this subject a wide 
field is open, and the youth of to-day, who are taking up 
this study, are destined to become the successful electrical 
engineers and inventors of the future. There is no better 
education for any boy, in the application and principles of 
electricity, than to begin at the very bottom of the ladder 
and climb up, constructing and studying as he progresses. 
When he attempts to design more technical and difficult 
apparatus the lessons learned in a practical way will be of 
inestimable value, greater by far than any theoretical prin- 
ciples deduced from books; he knows his subject from the 
ground up ; he understands his machine because he has con- 
structed it with his own hands. 

As I have said already, the necessary tools are few in num- 
ber and not expensive. They may include a hammer, a 
plane, awls, pliers, wire-cutters, and tin-shears. The raw 
material is also cheap — lead, tin, wire, wood, and simple 
chemicals. The laboratory may be a corner in the attic, or 
even in a boy's bedroom, so far as the finer work is con- 
cerned, while the hammering and sawing may be done in 
the cellar. The other best plan, of course, is to get the use 
of a spare room which may be fitted with shelves, drawers, 
and appliances for serious work. To enthusiastic beginners, 
as well as to those who have had some experience in elec- 
tricity, a needed warning may be given in three words: 

9 



ELECTRICITY BOOK FOR BOYS 

"Take no chances." Electricity, the subtle, stealthy, and 
ever-alert force, will often deal a blow when least expected. 
For that reason, a boy should never meddle with a high- 
tension current or with the mains from dynamos. The 
current in the house, used for lighting, cooking, or heating 
purposes, is always an attractive point for the young elec- 
trician, but the wires should never be touched in any way. 
Too many accidents have happened, and the conductors, 
lamp-sockets, and plugs should be carefully avoided. 

The boy should keep strictly to his batteries, or small 
dynamos run by water-power from a faucet; in no case 
should the wire from power-houses be tampered with. One 
little knows what a current it may be carrying and what 
a death-dealing force it possesses. Always bear in mind 
that a naked wire falling from a trolley equipment carries 
enough force to kill anything it strikes. 

Special attention is called to the dictionary of electrical 
terms given in the Appendix. The young student should 
never pass over a word or a term that he does not thor- 
oughly understand. Always look it up at once and every 
time it occurs, until you are sure that its meaning is fixed 
in your mind. This is an education in itself, at least so far 
as the theoretical knowledge of our subject is concerned. 

As a final word, I should like every boy interested in 
electricity to hear what Thomas A. Edison once said to me 
when I was a boy working in his laboratories. I often recall 
it when things do not go just right at first. 

I asked the great inventor one day if invention was not 
made up largely of inspiration. He looked at me quizzically 
for a moment, and then repHed: " My boy, I have little use 



SOME GENERAL EXPLANATIONS 

for a man who works on inspiration. Invention is two parts 
inspiration and ninety-eight per cent, perspiration." 

You will never get what you are after unless you work 
hard for it. You must stick to it until you produce results. 
If the history of the world's most valuable inventions could 
be fully known, the fact would be clearly established that 
the vital spark of inspiration is but the starting-point. 
Then follow the days, weeks, and sometimes years of 
industrious toil, failures, and disappointments, until finally 
the desired end is attained. One must work for success; 
there is no other means of winning it. 

As the table of contents shows, Part I. of this book 
explains principles and the simpler forms of electrical ap- 
pliances. From this we advance to Part II., which deals 
with more complex forms of electrical work, most of which, 
however, are within the reach of intelligent boys who have 
followed the chapters carefully from the first. In a final 
chapter we have simple explanations of the great commer- 
cial uses of electricity, which we see all about us, although 
very few of us have a clear idea as to their operation. 



Chapter II 

CELLS AND BATTERIES 

Simple Cells 

IN order to generate electricity it is necessary to employ 
cells, batteries, or dynamos. Since the construction and 
operation of a dynamo is somewhat intricate, it will be bet- 
ter to start with the simpler methods of electric generation, 
and so work up to the more complicated forms. For small 
apparatus, such as electric bells and light magnets and 
motors, the zinc-carbon-sal-ammoniac cell will answ^er very 
well; but for larger machinery, where more current is re- 
quired, the bluestone and the bi-chromate batteries will 
be found necessary. 

A simple and inexpensive cell may be made from electric- 
light carbons, with the copper coating removed, and. pencils 
of zinc, such as are used for electric-bell batteries and which 
can be purchased for five cents each. Copper wire is to be 
bound around the top of each pencil of carbon and zinc, 
and firmly fastened with the pliers, so that it will not pull 
off or become detached. It will be well to cut a groove 
with a file around the top of both the carbon and zinc, into 
which the wire will fit. The elements should then be 




SIMPLE BATTERY ELEMENTS 
13 



ELECTRICITY BOOK FOR BOYS 

clamped between two pieces of wood and held with screws, 
as shown in Fig. i . A more efficient carbon pole is made by 
strapping six or more short carbon pencils around one long 
one, as shown in Fig. 3. The short pieces of electric-light 
carbons are bound to the longest carbon with heavy elastic 
bands, or cotton string dipped in paraffine or wax, to make 
the cotton impervious to water and the sal-ammoniac 
solution. 

Another arrangement of elements is shown in Fig. 2, 
where a zinc rod is suspended between two carbons, the 
carbons being connected by a wire that must not touch the 
zinc. 

A fruit- jar, or a wide-necked pickle-bottle, may be em- 
ployed for a cell, but before the solution is poured in, the 
upper edge of the glass should be coated with paraffine. 
This should be melted and applied with a brush, or the edge 
of the glass dipped in the paraffine. 

The solution is made by dissolving four ounces of sal- 
ammoniac in a pint of water, and the jar should be filled 
three-fourths full. In this solution the carbons and zinc 
may be suspended, as shown in the illustration (Fig. 4) of 
the sal-ammoniac cell. The wood clamps keep the ca.rbon 
and zinc together, and the extending ends rest on the top 
of the jar and hold the poles in suspension. Plates of zinc 
and carbon may be clamped on either side of a square stick 
and suspended in the sal-ammoniac solution, as shown in 
Fig. 5 , taking care, however, that the screws used for clamp- 
ing do not touch each other. 

If one cell is not sufficiently powerful, several of them 
may be made and coupled up in series — that is, by carrying 

J4 



CELLS AND BATTERIES 



the wire from the zinc of one to the carbon of the next cell, 
and so on to the end, taking care that the wire from the car- 
bon in the first cell and that from the zinc of the last cell 
will be the ones in hand, as shown in Fig. 6. This consti- 
tutes a battery. Be sure and keep the ends of the wire 
apart, to prevent galvanic action and to save the power of 
the batteries. 

This battery is an excellent one for bells and small ex- 
perimental work, and when inactive the zincs are not eaten 
away (as they would be if suspended in a bi-chromate 
solution), for corrosion takes place only as the electricity 
is required, or when the circuit is closed. A series of bat- 
teries of this description will last about twelve months, if 
used for a bell, and at the end of that time will only require 
a new zinc and fresh solution. 

The cell in which the plates shown in Fig. 5 are used 
may contain a bi-chromate solution; and for experimen- 
tal work, where electricity is required for a short time 
only, this will produce a stronger current. But remember 
that the solution eats the zinc rapidly, and the plates 
must be removed as soon as you have finished using 
them. 

The bi-chromate solution is made by slowly pouring four 
ounces of commercial sulphuric acid into a quart of cold 
water. This should be done in an earthen jar, since the 
heat generated by adding acid to water is enough to crack 
a glass bottle. Never pour the water into the acid. When 
the solution is about cold, add four ounces of bi-chromate of 
potash, and shake or mix it occasionally until dissolved; 
then place it in a bottle and label it: 

15 . 



ELECTRICITY BOOK FOR BOYS 

BI-CHROMATE BATTERY FLUID 

POISON 

Before the zincs are immersed in the bi-chromate solution 
they should be well amalgamated to prevent the acid from 
eating them too rapidly. 

The amalgamating is done by immersing the zincs in a 
diluted solution of sulphuric acid for a few seconds, and 
then rubbing mercury (quicksilver) on the surfaces. The 
mercury will adhere to the chemically cleaned surfaces of 
any metal except iron and steel, and so prevent the cor- 
roding action of the acid. Do not get on too much mercury, 
but only enough to give the zinc a thin coat, so that it will 
present a silvery or shiny surface. 

A two-fluid cell is made with an outer glass or porcelain 
jar and an inner porous cup through which the current can 
pass when the cup is wet. Fig. 7. 

A porous cup is an unglazed earthen receptacle, similar 
to a flower-pot, through which moisture will pass slowly. 
The porous cup contains an amalgamated plate of zinc 
immersed in a solution of diluted sulphuric acid — one ounce 
to one pint of water. The outer cell contains a saturated 
solution of sulphate of copper in which a cylindrical piece 
of thin sheet-copper is held by a thin copper strap, bent over 
the edge of the outer cell. A few lumps or crystals of the 
copper sulphate, or bluestone, should be dropped to the 
bottom of the jar to keep the copper solution saturated at 
all times. When not in use, the zinc should be removed 
from the inner cell and washed off; and if the battery is 
not to be employed for several days, it would be well to 

16 



CELLS AND BATTE|^IES 



pour the solutions back into bottles and wash the several 
parts of the battery, so that it may be fresh and strong 
when next required. When in action, the solutions in both 




cups should be at the same level, ana be careful never to 
allow the solutions to get mixed or the copper solution to 
touch the zinc. Coat the top of 'he porous cell with par- 



17 



ELECTRICITY BOOK FOR BOYS 

affine to prevent crystallization, and also to keep it clean. 
Take great care, in handling the acid solutions, to wear old 
clothes, and do not let the liquids spatter, for they are 
strong enough to eat holes in almost anything, and even to 
char wood. The two-fluid cells are much stronger than the 
one-solution cells, and connected up in series they will de- 
velop considerable power. 

For telegraph-sounders, large electric bells, and as ac- 
cumulators for charging storage-batteries, the gravity-cell 
will give the most satisfactory results. The one shown in 
Fig. 8 consists of a deep glass jar, three strips of thin copper 
riveted together, and a zinc crow-foot that is caught on the 
upper edge of the glass jar. These parts will have to be 
purchased at a supply-house, together with a pound or two 
of sulphate of copper (blues tone). 

To set up the cell, place the copper at the bottom and 
drop in enough of the crystals to generously cover the 
bottom, but do not try to imbed the metallic copper in 
the crystals; then fill the jar half full of clear water. In 
another jar dissolve two ounces of sulphate of zinc in 
enough water to complete the filling of the jar to within 
two inches of the top; then hang the zinc crow-foot on the 
edge of the jar so that it is immersed in the liquid and is 
suspended about three inches above the top of the copper 
strip. The wire that leads up from the copper should be 
insulated with a water-proof coating and well covered with 
paraffine. A number of these cells may be connected in 
series to increase the power of the current, and for a work- 
ing-battery this will show a high efficiency. Note that at 
first the solutions will mingle. To separate them, join the 

i8 



CELLS AND BATTERIES 



two wires and start the action ; then, in a few hours, a divid- 
ing Hne will be seen between the white, or clear, and the 
blue solutions, and the action of the cell will be stronger. 
After long-continued use it may be necessary to draw off 
some of the clear zinc sulphate, or top solution, and replace 
it with pure water. The action of the acids reduces the 
metallic zinc to zinc sulphate and deposits metallic copper 
on the thin copper strips, and in this process an electrical 
current is generated. 

A Plange-battery 

When two or more cells (in which sulphuric acid, bi- 
chromate of potash, or other strong electropoions are em- 
ployed) are coupled in series, it would be well to arrange the 
copper and zinc, or the zinc and carbon, poles on a board, 
so that all of them may be lowered together into the solu- 
tions contained in the several jars. A simple arrangement 
of this kind is shown in Fig. 9, where a rack is built for the 
jars and at the top of the end boards a projecting piece of 
wood, supported by a bracket, is made fast. A narrow piece 
of board nearly the length of the jar-rack is fitted with the 
battery-poles, as shown at Fig. 9 A. The carbon and zinc, 
or copper and zmc, poles are attached to small blocks of 
wood (as described for Fig. 5), and this block in turn is 
fastened to the under side of the board with brass screws. 
The poles of the cells are to be connected (as explained in 
Fig. 6), and when the battery is in use the poles are immersed 
in the solution contained in the jars. When the battery is 
at rest the narrow board should be lifted up and placed on 

19 



ELECTRICITY BOOK FOR BOYS 

the projecting arms of the rack, so that the Hquid on the 
poles may drain into the jars directly underneath. One or 
more of these battery-racks may be constructed, but they 
cannot be made to hold conveniently more than four or six 
cells each ; if more cells are required, those contained in each 
rack must be coupled up in series. 

A simpler plunge-battery is shown in Fig. lo. A cell- 
rack is made of wood and given two or three coats of 




shellac. The narrow board (to the under side of which the 
battery-poles are attached, as explained in Fig. 9) is hung 
on chains or flexible wires, which in turn are made fast to 
an iron shaft running the entire length of the cell-rack. 
This shaft is of half-inch round iron, and is held in place, 
at one end, by a pin and washer; while at the other the end 
is filed with a square shoulder, and a handle and crank is 
fitted to it, so that the shaft may be turned. A small hole, 
made at the side of the crank when it is hanging down, will 
receive a hard- wood peg, or a steel nail, and this will pre- 
vent the crank from slipping when the board holding the 



20 



CELLS AND BATTERIES 

poles is raised. If a gear-wheel and tongue can be had to fit 
on the shaft, it will then be possible to check the shaft 
securely at any part of a turn of the crank. The battery- 
poles are to be connected in series along the top of the 
portable board, as explained for Fig. 6. When two or more 
of these plunge-batteries are used at one time, the wire from 
the carbon of one is to be connected with the zinc pole of 
the next, and so on. The wire from the zinc of the first 
battery, and the wire from the carbon of the last battery, 
will be the ones available for use. 

A Storage-battery 

When more current is desired than the simple batteries 
will give, a storage-battery should be employed as an ac- 
cumulator. This result can be secured by coupling pri- 
mary cells in series, so that they will be constantly generat- 
ing and feeding the battery. Storage-batteries are too heavy 
to be shifted about, like single cells or small plunge-batteries ; 
they should be placed in a cellar, where the charging or 
primary cells can be located close by, and, unless positively 
necessary, the battery of cells and the accumulator should 
not be moved. 

With sufficiently large insulated wires (Nos. 12, 14, or 16 
copper) , the current may be carried to any part of the house 
for use in various ways — such as running a light motor or 
a fan, lighting a lamp-circuit, or fusing metals and chemicals 
for experimental purposes. While the battery to be de- 
scribed is not a light one in weight, nor as economical as the 
improved new Edison storage-battery, it is a good and 

21 



ELECTRICITY BOOK FOR BOYS 

constant one, and, if not overcharged or abused, will last 
for several years. 

The component parts of a storage-battery are lead in 
metallic and chemical form, the electrolyte, or fluid, in 
which the plates are immersed, and the water-tight and 
chemical-proof cell or container. From a plumber, a sup- 
ply-house, or a lead- works, obtain a quantity of three-eighth 
by one-quarter-inch strip-lead of the kind called chemical, 
or desilverized; also a larger quantity of lead- tape, one- 
sixty-fourth of an inch thick and three-eighths of an inch 
wide. This last is also known as torpedo-lead, and is kept 
by electrical supply-houses. 

If the three-eighths by quarter-inch strip-lead cannot be 
had, then purchase eight or ten pounds of heavy sheet-lead, 
and, with a tin-shears, divide it into strips three-eighths of 
an inch wide and twenty-nine inches long, taking care to 
cut it of uniform width and with true edges. From hard- 
wood three-eighths or half an inch thick, cut a block six 
by seven inches and make four countersunk holes in it, so 
that it may be screwed fast to a table or bench, as shown in 
Fig. II A. Around this the lead strips should be shaped 
and beaten at the corners to make the angles sharp. 

From the three-eighths by quarter-inch, or sheet-lead 
strips, make seven frames as shown in Fig. 12. This is done 
by binding a strip of the lead around the block, as shown 
at Fig. II B. Where the ends come together insert a short 
piece of lead, three-eighths or half-inch, as shown at Fig. 
12 A, and solder it fast. A soldering-iron may be heated 
with a Bunsen-burner gas-flame or in a charcoal fire. How- 
ever, if gas is available, it would be better to use the blue 



CELLS AND BATTERIES 



flame from a Bunsen burner and direct the hot blast directly 
on the work with a blow-pipe, and so fuse the lead points 
together. After a little practice with the blow-pipe it will 
be used for many pieces of work in preference to the solder- 





^^'^^^ 




B 




D 



ing-iron. If the sheet-lead is used for the frames in place of 
the three-eighths by quarter-inch strips, two or three strips 
will have to be taken, so as to build up the band of the frame 
to about a quarter of an inch in thickness. When soldered 
together, or fused at the edges, these built-up frames will be 
as rigid as the solid metal. 

Now cut a number of strips of the thin lead- tape six inches 
and a half long, and others that will necessarily be somewhat 
longer, for each frame is to be filled with straight and 
crimped pieces, as shown in Fig. 13. If there is a flu ting- 
iron in the house, the crimping may be done in the brass 
gears at one end of the machine. Or two wheels may be 
cut from hard-wood with a fret-saw, and made fast to a 

23 



ELECTRICITY BOOK FOR BOYS 

block with screws, as shown in Fig. 14. A handle, attached 
to one wheel, will make it possible to turn the gears; and 
they should be placed just far enough apart to allow the 
tape to pass through without tearing or squeezing. Put a 
washer between the wheel and the block to prevent friction. 

When a frame is in the position shown in Fig. 13, and 
lying on a piece of slate or flat stone, you will first put in a 
crimped piece of tape, as shown at Fig. 13 A, and under this 
arrange a straight piece (Fig. 13 B); then, with the blow- 
pipe and flame, fuse fast to the frame and catch the flutes 
of the crimped piece to the straight one every inch or two. 
Add alternate crimped and straight strips iintil the frame 
is filled and presents the appearance of Fig. 13. When the 
seven frames are ready, lay three of them aside for the 
positives and four for the negatives. Note that the posi- 
tives are red and the negatives a dark yellow when they are 
filled with the active material. 

There are several methods of depositing the active mate- 
rial in the mesh or net- work of the plates, but some of them 
are too technical, others too complicated, and still others 
require charging machinery. The following plan will be 
the simplest and easiest for the amateur : 

At a paint-store, or from a wholesale druggist, obtain 
several pounds of oxide of lead (red-lead) and a similar 
quantity of litharge (yellow-lead). In an earthen vessel, 
or large jar, make a solution composed of water, twenty 
ounces, and commercial sulphuric acid, two ounces. This 
is the mixture commonly known as "one to ten." Place 
some red-lead (dry) in an old saucepan or soup-plate, and 
add a little of the acid solution: then, with an old table- 

24 



CELLS AND BATTERIES 



knife or small trowel, mix the lead into a stiff paste, like 
soft putty. Do not get it too thin or it will run; nor too 
thick, as then it will not properly adhere to the lead-mesh 
of the frames. With the frame lying on its side, plaster 
in the red composition between the flutes and fill up the 
frame solid with it. Treat all three of the positive frames 
in the same manner, taking care that the exposed surfaces 
of the composition-filling is smooth and flush with the edges 
of the lead frame and mesh. Do not disturb these plates 
for a while, but let them remain in position, so as to set and 
partially dry. Add acid solution to the yellow-lead in a 
similar manner, and fill the four negative plates. When 
partially dry, the plates will be ready to combine in a pile. 
At a supply-house obtain some sheets of cellulous fibre, 
three-sixteenths of an inch thick, or some asbestos cloth. 
If neither can be had, then soak some pieces of ordinary 
brown card-board in a solution of silicate of soda and let 
them dry. Lay a negative (yellow) plate on the table with 
the lug at the left (Fig. 13 C). On this place a square of 
the fibre, asbestos, or card-board; and on top of it lay a 
positive (red) plate with the lug at the right side. Continue 
in this manner until the seven plates are stacked, the four 
negative lugs being at the left and the three positives at 
the right. Tie the plates securely together with cotton 
string bound about them in both directions ; then stand the 
pile up so that the lugs are at the top, as shown at Fig. 1 5 , 
with every alternate lug in an opposite direction. Obtain 
two lead bars three-eighths of an inch square, or cut strips 
from the sheet-lead and solder them together, turning the 
ends as shown at Fig. 13 D. Drop one of these bars into 

25 



ELECTRICITY BOOK FOR BOYS 

the lugs of the positive plates, as shown in Fig. 15 H, and 
solder it fast at the three unions. Repeat this with the 
other bar in the lugs of the negative plates, and the pile will 
then be ready for immersion in the electrolyte. To both 
ends of each plate-bar solder binding-posts, so that the con- 
ductor-wires can be attached at one end and the feed-wires 
at the other. If a hard rubber or glass cell can be had for 
the battery so much the better ; if not, a stout box may be 




CELLS AND BATTERIES 



made from pine, white-wood, or cypress, and thoroughly- 
coated with asphaltimi varnish or asphaltick. At an elec- 
trical supply-house you can purchase some ' ' P and B ' ' 
compound, which is acid and water proof. This is excellent 
for the inside coating as well as for the outside of the box. 

The box should be made of wood not less than three- 
quarters of an inch thick, and the sides, ends, and bottom 
should be in one piece, free from knots, sappy places, or 
cracks. Brass screws should be used to hold the boards 
together, and before the joints are made the butt-ends of 
wood and the sides, against which they impinge, must be 
thoroughly coated with the asphaltimi or compound. Put 
together the four sides first and then make the bottom fast, 
placing the screws two inches apart and countersinking the 
wood, so that the screw-heads will lie flush, as shown in Fig. 
1 6. The box should be large enough to allow about one 
inch of space all around the pile, and deep enough for the 
solution to cover the plates and two inches of space above it 
to the top edge of the cell. The complete storage-battery 
will then appear as shown in Fig. 17. 

The electrolyte is composed of sulphuric acid and water 
in the proportion of one ounce of acid to four of water, 
making a five-part solution. This should be mixed in an 
earthen or glass jar, and the acid poured slowly into the 
water, the latter being stirred while the acid is added. 
When the solution cools (for adding acid to water creates 
heat), add about two ounces of bicarbonate of soda, and 
mix the solution thoroughly. 

When the pile is in place within the box (having first 
removed the string which bound the plates together) pour 

27 



ELECTRICITY BOOK FOR BOYS 

the electrolyte slowly into the cell, taking care that none of 
it spatters, for it will eat clothing or anything else that it 
touches. Before placing the pile, or electrolyte, in the box, 
it should be thoroughly tested for leaks by allowing water 
to stand in it for several days. Indeed, you should be very 
generous with the asphaltum, or compound, when coating 
the angles and points inside the box ; for if the acid solution 
gets at the screws it will corrode them and the box will soon 
leak and fall apart. As a precaution against the acid work- 
ing over the top of the box, the upper edge, for an inch or 
two, should be coated with parafhne over the asphaltum or 
acid-proof coating. 

A cell constructed in this way should accumulate about 
two volts and one hundred ampere-hours, and will run a 
one-sixteenth horse-power motor. The expense of making 
these plates is about twenty-five cents each, and, including 
the cell and coating materials, each storage-battery will cost 
approximately two dollars. The lasting qualities of the 
battery depend on the use or abuse it is put to ; but with 
ordmary care it should last from three to five years. 

When the battery ceases to accumulate properly the pile 
should be removed, and, after washing it thoroughly, the 
bars should be cut away and new positive plates made and 
installed. The positive plates are the ones that deteriorate 
and need replacing; the negatives are almost everlasting, 
and with proper usage will live for fifteen or twenty years. 

Directly the electrolyte is in the cell, connect the poles of 
your primary cells so as to begin the accumulation of cur- 
rent. Never exhaust the charge of electricity from your 
storage-cell, and never leave it uncharged when the electro- 

28 



CELLS AND BATTERIES 



lyte is in, or the plates will be ruined. A battery consisting 
of from five to twenty bluestone cells will be the best with 
which to charge this accumulator ; and if more than one cell 
is desired, any number of them can be made and coupled 
up in series. Take care, when connecting the wires from 
the primary cells, to see that the positive wire is connected 
with the positive plates and the negative with the lead bar 
joining the yellow plates. If by accident you should make 
a misconnection, bubbles will rise from the electrolyte. This 
is not right, so reverse the wires and the accumulation of 
current will then take place without agitation in the cell. 



Dry-ccIIs and Batteries 

Dry-cells are extensively used nowadays, since their clean- 
liness, high efficiency, and low internal resistance make them 
preferable to the Leclanche and other open-circuit bat- 
teries for bells, annunciators, and other light work. In the 
dry-cell, the electrolyte, instead of being a liquid, is a gela- 
tinous or semi-solid mass, which will not run nor slop over. 
When the capping of pitch or tar is in place, the cell may be 
placed in any position, with full assurance that the electro- 
lyte will not become displaced nor run out. Dry-cells may 
be made of almost any size for convenience of handling, but 
those commonly used vary from one to four inches in diam- 
eter, and from four to fifteen inches high. For bells and 
general electric work, a cell two inches and a half in diameter 
and seven inches high will be found a convenient size to 
make and handle. 

29 



ELECTRICITY BOOK FOR BOYS 



The component parts of a dry-cell are the cell itself (which 
is made of zinc and acts as the positive pole), the carbon, the 
electrolyte or active excitant element, and the pitch or tar 
cap to hold the electrolyte and carbon in place. 

From a tinsmith obtain some pieces of sheet zinc, and roll 
them into cylindrical form as shown in Fig. i8 A. The 
sheets should measure seven by eight inches, and when 
formed the edges are to be lapped and soldered. 

From a smaller piece of 



Tiq-ia 





zinc cut round bottoms, fit 
them in the cylinders and 
solder securely in place, 
taking care to close up 
all seams or joints to pre- 
vent the escape of the 
electrolyte. 

From a supply-house ob- 
tain battery - carbons, one 
inch and a half wide by 
half or three - eighths of 
an inch thick and eight 
inches long. These should be provided with a thumb-screw 
or small bolt and nut at the top so as to make wire connec- 
tions with the carbon. A strip of zinc should be soldered 
to the outside upper edge of the zinc cup to which wire 
attachments may be made with thumb-screws or small bolts 
and nuts. When the parts are ready to assemble, make a 
wooden mould or form a trifle larger than the carbon. This 
is intended to act as a temporary plunger, and is inserted, 
at first, in place of the carbon plate. This wooden plunger 

30 



CELLS AND BATTERIES 

should be smooth, and given a coat of shellac to prevent it 
from absorbing any moisture. 

Insert the plunger in the zinc cup and support it so that it 
will be at least half an inch above the bottom and centred 
at the middle of the cup. The electrolyte is then placed in 
the cup, and, when it has set a little, the wooden plunger 
is removed and the carbon inserted in its place. 

The electrolyte is composed as follows : 

Ammonium chloride i part 

Zinc chloride . . . i part 

Plaster of Paris 3 parts 

Flour f part 

Water 2 parts 

Mix these together and place the compound within the zinc 
cups, so that the mass settles down and packs closely about 
the plunger. The space left unfilled about the carbon 
should be filled with a mixture composed as follows : 

Ammonium chloride i part 

Zinc chloride i part 

Manganese binoxide i part 

Granulated carbon i part 

Flour I part 

Plaster of Paris 3 parts 

Water 2 parts 

These proportions may be measured in a tin cup, a table- 
spoon, or any other small receptacle. Note that the meas- 
urement by parts is always by bulk and not by w^eight. 

Do not fill the zinc cup to the top, but leave an inch of 
space, so that half an inch of sealing material may be added. 
See that the inside top edge of the zinc cup is clean; then 

31 



ELECTRICITY BOOK FOR BOYS 

melt some tar or pitch and pour it over the top of the elec- 
trolyte, so that it binds the zinc cup and carbon into a solid 
form. Drive an awl down through the capping material 
when it is nearly dry, and leave the holes open for the 
escapement of gases. 

Give the outer surface of the zinc cells a coat of asphaltum 
varnish, and wrap several thicknesses of heavy paper about 
them to prevent contact and short-circuiting. Protect the 
bottoms in a similar manner, and as a result you will have 
a cell that will appear as shown in Fig. t8 B. A battery 
of cells powerful enough for any light work can be made 
by connecting the cells in series, each having an electro- 
motive force of one and a half volts, with an internal re- 
sistance of less than one-third of an ohm. 



Chapter III 

PUSH-BUTTONS AND SWITCHES 

Pttsh-btfttons 

PUSH-BUTTONS and switches are a necessity in every 
home where electric bells, lights, or fans are used, for 
with them connections are made or broken. The telegraph- 
key and the commutators on a motor and dynamo are only 
improved forms of the push-button, and this simple little 
device is really an indispensable part of any electrical equip- 
ment. 

The simplest form of push-button is a bent piece of tin or 
thin sheet-metal screwed fast to a small block of wood, as 
shown in Fig. i. Under the screw-head one end of a wire 
is caught, and the other wire end is secured by a washer and 
a screw driven into the block directly under the projecting 
end of the strip of metal. By pressing a finger on the tin 
it is brought into contact with the screw-head imder it, and 
the circuit is closed ; on releasing it, the tin flies up and the 
circuit is opened again. 

An enclosed push-button is shown in Fig. 2. It is made 
of the cover or body of a wooden box, a spool-end, and sev- 
eral other small parts. A round piece of thin wood is cut 
to fit inside the box and so form the base for the button. 
3 33 



ELECTRICITY BOOK FOR BOYS 

On this the spring strip is attached with screws, and the 
wire ends are made fast, as shown in Fig. 3. The wires are 
carried through the bottom of the base and along grooves to 
the edge, and thence to their final destination. The end of 
a spool is cut off and glued to the top of the box, as shown 
in Fig, 2, and a hole is made in the box to correspond in size 
with that in the spool. Through this aperture the button 
(cut from a wooden dowel or shaped out with a knife) passes, 




TiCrS 



TiQ^A 



so that the end projects about a quarter of an inch beyond 
the spool. To prevent the button from falling out, a small 
steel nail should be driven across the inner end, or a washer 
may be tacked to the end of the stick, as shown in Fig. 4. 

The button is mounted by screwing the base fast to the 
door or window casing, it being understood that the wires 
have been first arranged in place. The button is then set 

34 



PUSH-BUTTONS AND SWITCHES 

in the hole and the cap is placed over the base, covering it 
completely. By means of small screws, passed through the 
rim of the box and into the edge of the base, the cap is held 
in place. A coat of paint or varnish will finish the wood- 
work nicely, and this home-made button should then an- 
swer every requirement. 

Switches and Ctrt-outs 

In electrical equipment and experimental work, switches 
and cut-outs will be found necessary, particularly so for 
telegraph and telephone lines. Care should be taken to 
construct them in a strong and durable fashion, for they 
will probably be subjected to considerable wear and tear. 

A simple switch (Fig. 5) is made from a base-block of 
wood three inches long, two wide, and half an inch in thick- 
ness, together with some small metal parts. It has but one 
contact-point, and that is the brass-headed tack (T in Fig. 5) 
driven through the binding-post, the latter being a small 
plate of brass, copper, or even tin screwed to the base-block. 
The end of a wire is caught under the screw-head before it 
is driven down. A similar binding-post is arranged at the 
lower side of the block, and the movable arm is attached to 
it with a screw. Between the arm and the post-plate there 
should be a small copper washer, to make it work more 
easily. The arm is cut from a thin piece of hard sheet brass 
or copper (tin or zinc will also answer very well) , and at the 
loose end the half of a small spool is attached, with a brass 
screw and washer, to ser\'e as a handle. The end of the 
screw that passes through a hole in the arm is riveted to the 

35 



ELECTRICITY BOOK FOR BOYS 

tinder side to hold it securely in place. This arrangement 
is shown in Fig. 6. 

The under edges of the arm may be slightly bevelled with a 
file, so that it will slip up easily on the oval head of the brass 
tack. The drawing shows an open switch ; when the circuit 




is closed the arm rests on the tack-head. By means of small 
screws this switch-board may be fastened to a table or to 
any part of the wood- work in a house. 

In Fig. 7 a complex switch is shown. This is the principle 
of the shunt-box switch, of the resistance-coil, and also of 
the commutators of a motor. A motorman's controller on 
a trolley-car is a good example of the shunt, and, with it 
and the resistance-coils, the car can be started, stopped, or 
run at any speed, according to the current that is admitted 
to the motor. 

The complex switch is made in the same manner as de- 
scribed for the single switch, except that any number of 
binding-posts may be employed, arranged on a radial plan, 
so that the end of the arm will rest on any tack-head at will. 
Bells in various parts of the house may be rung by this 

36 



PUSH-BUTTONS AND SWITCHES 

switch, or it may be coupled with a series of resistance-coils 
to control any amount of current. 

The simple cut-out (Fig. 8) is constructed in the same 
manner as the simple switch, except that there are two 
points of contact instead of one. This is the principle of 
the telephone and telegraph instrument wiring, so that a 
bell or sounder may be rung from a distance. The arm is 
then thrown over and the bell cut out, allowing the " phone " 
or key to be brought into use. In lifting the transmitter 
from the hook on a telephone, a cut-out is operated and 
the bell circuit is thrown out of action. It is in operation 
again directly the transmitter is returned to the hook. 
The switch cut-out (Fig 9) is inactive when the arm is in 
the position shown in the illustration ; but when it is thrown 
over (as shown by the dotted line) it connects the poles at 
opposite ends of the board. It may be thrown over in both 
directions, and is a useful switch for many purposes. 

For strong currents the lever-switch, that rests on a brass 
tack-head, will not be suitable, as the switch -bar must be 
held firmly in place to make a perfect connection. Strong 
currents throw weak switches open, causing an open or 
broken circuit. 

A single pole-switch, to carry a current up to one hundred 
and twenty-five volts and twenty-five amperes, is shown in 
Fig. 10. This consists of a base-block, a bar which is at- 
tached to the vertical ears of a binding-post, and a clutch 
that will hold the bar when it is pressed down between the 
ears. 

The base-block should be made from some non-conducting 
material, such as soapstone, marble, or slate. If a piece of 

37 



ELECTRICITY BOOK FOR BOYS 

soapstone can be procured, that will be just the thing, since 
it is easily worked into the proper shape and size. Soap- 
stone may be sawed and smoothed with a file ; it is easily 
bored into with a gimlet-bit, and it is one of the best non- 
conducting substances. The base for this switch is six 
inches long, two inches wide, and as thick as the soapstone 
happens to be — say three-quarters of an inch. The top 
edge may be bevelled for the sake of appearance or left 
square. 

Two pieces of heavy sheet copper or brass are to be cut 
as shown at A in Fig. ii. The ears are half an inch wide, 
and the total height of the strip is two inches and a half, 
while the part with two holes in it side by side is one inch 
and a quarter long, including the half -inch width of the 
vertical strip. With round and flat-nosed pliers bend the 
long ears into shape, so as to form a keeper for the bar which 
is then to be riveted in place. Omit the holes at the ends 
of the long ears in the other plate ; then bend it into shape 
to form a clutch that will hold the bar when it is pressed 
down between the ears. These binding-posts should be 
made fast to the base-block with brass machine-screws and 
nuts, which will fit in countersunk holes in the bottom of 
the soapstone. If hard-wood is used for the base, ordinary 
brass wood-screws will answer very well. 

The connection-bar is cut from metal the same thickness 
as that employed for the binding-posts and clutches; it 
should be shaped so as to appear as shown at B in Fig. 1 1 . 
A handle should be driven on the slim end, and where the 
lower edge enters between the ears of the clutch, the corners 
of the bar should be rounded with a file. Countersunk 

3^ 



PUSH-BUTTONS AND SWITCHES 

screw-holes are bored in the base, so that it can be made 
fast to the wood-work. 

A double pole-switch is shown in Fig. 12, and in general 
construction it is similar to the vSingle pole-switch described 
above. The binding posts and bars are cut and bent from 
the patterns A and B in Fig, 1 1 ; but in this case the long, 
slim ends of the bars are omitted. A short turn is made at 
the handle end of each bar and a hard-wood block is placed 




ri(T.i2 



between the bar-ends and held in position with screws 
driven through holes made in the bars and into the ends of 
the block. A handle is made fast to the middle of the block 

39 



ELECTRICITY BOOK FOR BOYS 

with a long and slim wood-screw; or a steel -wire nail may 
be passed through the handle and block, a burr slipped over 
the end opposite the head, and the small end riveted fast. 
When the binding-posts (to which the ends of the bars are 
attached) are screwed onto the base, be sure and see that 
the bars are parallel and the same distance apart at both 
ends. In like manner, when the cleat binding-posts are 
made fast, see that they are directly in line with the bars, 
so that the yoke will drop into the spaces between the ears 
without having to be pulled to one side or the other. This 
is a very useful switch for strong currents, and may be 
placed close to a dynamo, so that the current in both wires 
may be cut out at once. 

Table-jack Switches 

A table- jack switch is a most convenient piece of appa- 
ratus where several lines of bells, alarms, or telephone cir- 
cuits are to be switched on and off. 

The single table-jack switch, shown in Fig. 13, is made of 
a hard-wood block three-quarters of an inch thick, five 
inches wide, and seven inches long. It is to be smoothed 
and varnished, or given several coats of shellac. At the 
four corners small holes are made to receive slim screws, 
and at one end of the block five short metal plates are 
screwed fast, with the heads of the screws countersunk, so 
that they will be flush with the top of the plates. These 
small plates should be half an inch wide and one inch long, 
and may be of brass, copper, or tin. But if they are of tin 
the plates are made of a longer strip tacked to the board 

40 



PUSH-BUTTONS AND SWITCHES 

and then bent over, as shown at A in Fig. 14. They will 
therefore form short springs, the upper parts of which will 
rest against the long spring-arms. From spring brass or 
copper five arms are to be cut and shaped, as shown in 
Fig. 13. Holes are made at one end of each, and others 
again two inches from these, through which to pass screws. 

Screw-eyes are passed through copper washers and the 
end holes in the strips, and then screwed into the wood plate. 
These will act as binding-posts, while the second line of 
screws will hold the plates down to the base. The arms 
should be bent, so that when the screws are driven down the 
lower edge will press on the small plates under them. 

The outlet wires are attached to the binding-posts at the 
head of the block, and the plug (A in Fig. 13) is inserted 
between the arm and plate at the foot, so that contact and 
connection are made. This plug is a small plate of metal to 
which the end of a flexible wire is made fast. It should be 
of copper or brass, but for light work a strip of tin may be 
bent over with the wire caught between the plates and a 
copper tack passed through the sides and riveted, as show^n 
at B in Fig. 14. 

A double jack-switch (Fig 15) is made on the same general 
plan as the single, but it has no binding-posts. A block of 
the same size is used, and two rows of short plates are made 
fast at each end. The arms are made with two screw-holes 
near the middle, as shown in Fig. 15, and through these 
holes screws are driven to hold the arms down to the base. 
Several plugs are used for each end, so that the in and out 
lines can be shifted, and frora one to four lines used at a 
time. 

41 




TABLE-JACK SWITCHES 
42 



PUSH-BUTTONS AND SWITCHES 

A convenient slip-switch for single or double line work 
is shown in Fig. i6. This consists of a small wooden base, 
on which a brass arm and handle are screwed fast and 
connected with a binding-post (A in Fig. i6). A slip-plate 
is made from a piece of sheet-brass and bent so as to form 
a pocket into which the arm will fit. This pocket piece is 
connected with the binding-post B. When the switch is 
thrown out the circuit is broken, unless a contact-point, C, 
is provided, from the under side of which a wire leads out 
to a second circuit. When the switch is in place, as shown 
in Fig. 1 6, the circuit is closed through A and B ; but when 
the arm is thrown out the circuit through A and B is broken 
and that through A and C is closed. 

Binding-posts and Connectors 

To make quick connections between wires and other 
parts of electrical apparatus, binding-posts are the most 
convenient device, since the turn of a screw binds or releases 
a wire instantly. Binding-posts may be made in many 
forms, but the simple ones that a boy will need can be made 
from screw-eyes, burrs, stove-bolts, and nuts, together with 
thin strips of metal and nails. 

Five simple posts are shown in Fig 17. A is made from 
a screw and two burrs, B from a screw-eye and two burrs, 
and C from a thin plate of metal and two screws, with oval 
or round heads. This last, however is more of a connector 
than a binding-post. The ends of the wires to be connected 
should be caught under the screw-heads or between the 
burrs before the screws are driven down. 

43 



ELECTRICITY BOOK FOR BOYS 

In D a simple arrangement of a stove-bolt and two nuts 
is shown. The under bolt is screwed down tightly against 
the wood, and under the head a wire is made fast, so that 
another wire may be caught under the upper nut. If a 
small thumb-nut can be had in place of the plain nut, it will 
be easier to bind the upper wire. In Fig. 17 E a thin 
strip of metal may be folded over, and at the loose ends a 





hole should be punched through which a screw-eye will 
pass. The metal is held to a wood base with a screw, under 
the head of which a wire is caught. The second wire end is 
slipped between the metal plates, and a turn of the screw- 
eye will bind and hold it securely. 

Connectors are employed to unite the ends of wires 
temporarily, and are made in many forms. A simple and 
useful one is made from a piece of spiral spring fastened to 
a block of wood by two staples, as shown at Fig. 18 A. 

44 



PUSH-BUTTONS AND SWITCHES 

The ends of the wires are pressed down into the coils of the 
spring and are held with sufficient security for temporary 
use. Another connector is made from a block of wood, a 
strip of thin metal, and two screw-eyes (Fig. i8 B). The 
metal is bent around the ends of the block, and through 
holes made in the ends of the strip screw-eyes are driven into 
the block. When the ends of wires are slipped under the 
metal, a turn of the eyes will hold them fast, as shown at 
Fig. 1 8 B. 

A short bolt threaded at each end. and provided with four 
nuts will also act as a connector. The inner nuts are screw- 
ed on tightly and the outer ones are loose, so that when 
wires are placed between them they may be tightened with 
the fingers, as shown at C in Fig. i8. These are a few sim- 
ple forms of connectors ; the ingenious boy can devise many 
others to suit his needs and ideas. 

Lightning-arresters and Ftise-blocks 

All lines of exposed wire that run from out -doors into 
the house should be provided at both ends with lightning- 
arresters, particularly if they are telephone or telegraph 
lines, burglar alarms, or messenger call-boxes. In many 
instances where improtected telephone lines have been the 
plaything of lightning, painful accidents have happened, 
and it is only the part of prudence to provide against them. 
It is better to have an arrester at both ends of a line, and 
as the cost is insignificant it is hardly worth considering as 
against its feature of safety. 

Lightning-arresters may be constructed in many ways 

45 



ELECTRICITY BOOK FOR BOYS 



and of different materials; the ones here shown and de- 
scribed are easily made and efficient. The principle of all 
arresters is simply a fuse which burns out whenever the wire 
is carrying a greater amount of current than is required for 
the proper w^orking of the apparatus, thereby arresting the 
current and protecting the instruments from destruction. 
Induction-coils, relays, fine windings on armatures, or a 
magnet helix are quickly destroyed if a too powerful cur- 
rent is permitted to pass through them, and it is therefore 
advisable to protect them. When a fuse burns out under a 
trolley-car, or in the shimt-box of a motor-car or engine, 
it is because a greater amount of current is trying to pass 
in than the motor will safely stand. When a fuse ''blows 
out," the apparatus or motor is put out of commission until 
the fuse is replaced, but the delicate mechanism and the fine 
wiring on the field-magnets or armatures are saved. 

The simplest form of single pole-fuse is a fine piece of 
lead wire held between two binding-posts, as shown at A in 
Fig. 19. The lead wire may be of any length ; but for small 
instruments, where a moderate current is employed and 
where there is a possibility of lightning travelling on the 
wire, the fuse should be from two to three inches long. 
For inside work, however, where it is to be used simply as 
a safety, the wire may be shorter and finer. 

To make the lightning-arrester shown in Fig. 19, cut out 
a hard-wood block five inches long, an inch wide, and half 
an inch thick. Give this several coats of shellac ; then place 
a piece of mica, or asbestos paper, over the top of the block, 
and make it fast with thick shellac to act as a glue. From 
small pieces of copper or brass cut two plates one-half by 

46 



PUSH-BUTTONS AND SWITCHES 

one inch, and drill holes in them to take screws and screw- 
eyes. Place copper burrs under the screw-eyes for connect- 
ors, and drive two brass screws half-way down in the block 
through the holes at the inner ends of the binding-post 
plates. See that these screws fit snugly in the holes in the 
plates so that contact is perfect. If the holes are too large 
and the screws fit loosely, two copper burrs will have to be 
used and the screws driven in, so that the heads bind the 
burrs on the ends of the fuse-wire. From an electrician, or 
supply-house, purchase a few inches of fine lead fuse- wire — 
say Nos. 20, 22, or 24 — and twist the ends of a length aroimd 
the screws, as shown in the drawing. Perfect contact should 
be had between the lead wire and the screws; by way of 
precaution, a bit of solder will dispel all doubt. Just touch 
the point with a little soldering solution; then apply a 
soldering-iron having a drop or two of solder on the end. 

Perfect connection is absolutely necessary for telephone, 
telegraph, or annunciator work, and where there is a light- 
ning-arrester and the line is not working well, the trouble 
may often lie in the poor contact of lead and brass or cop- 
per, or possibly in using wire that is too fine. Lead is a very 
poor conductor, and a fine wire would act as a check. For 
a test, first insert a piece of copper wire to see that the line 
is working properly ; then use lead wire of sufficient size to 
carry the current as well as the copper did. The action of 
metals and wire, as current retarders, will be explained in 
the chapter on resistance and resistance-coils. 

For general commercial use the base-blocks of all light- 
ning-arresters should be made of porcelain, slate, or some 
of the composition non-conductors, such as moulded mica, 

47 



ELECTRICITY BOOK FOR BOYS 

silex and shellac, or fibre. As these are not always availa- 
ble, wood, with a covering of mica, will answer every pur- 
pose and can be readily adapted for use. 

The apparatus pictured in Fig. 19 is known as a single- 
pole lightning-arrester, and is the simplest form of this kind 
of electrical paraphernalia. In Fig. 20 a double-pole ar- 
rester is shown. This is constructed in the same manner 
as described for the single one. The block is five inches 
long, two inches wide, and half or five-eighths of an inch 
thick. A countersunk hole is made in the middle of all the 
lightning-arrester blocks through which a screw can be 
passed to hold the apparatus fast in any desired location. 

In Fig. 21 another form of fuse is shown. It is made 
from a piece of mica three-quarters of an inch wide and four 
inches long, two pieces of thin sheet-copper, and a piece of 
lead fuse-wire. The copper is three-quarters of an inch 
wide, and one piece of it is bent in the form of a V, as shown 
at A in Fig. 2 1 . One end of the mica strip is dropped in the 
V, and with a pair of pliers the V is closed up by pinching 
it at the bottom. To further insure its staying in place, the 
top and end, or open edges, should be soldered. Punch a 
small hole through the copper ends, at the inside edge, slip 
the ends of the fuse-wire in them, and touch the union with 
a drop of solder to insure perfect contact. With shears and 
file cut a U from the side of one copper band and from the 
end of the other; these will allow the copper ends to pass 
under the heads of screws, thus avoiding the necessity of 
removing the entire screw from the block in order to set the 
fuse in place. 

The block on which this fuse is held is shown in Fig. 22, 

48 




fi^i9 Q^M 



T\<jzo 





(C^ 



Ti^2i- 




7i(5.23 



LIGHTNING-ARRESTERS AND FUSE-BLOCKS 
49 



ELECTRICITY BOOK FOR BOYS 

and is made in a similar manner to the one shown in Fig. 19, 
except that the metal plates are a trifle longer and are 
bent up, as shown in the drawing. Thus the mica fuse-plate 
will be elevated above the block. If the brass or copper 
used for the binding-post plates is too thin to stand the 
pressure of the screws when the fuse ends are screwed fast, 
put a few burrs on the screws below the plates; then the 
pressure of the screws cannot bend down the extending ears 
of the plates and make an imperfect contact. 

Another form of fuse-block is shown in Fig. 23. The 
same sort of a fuse is employed as shown in Fig. 21, but 
without the U cuts at the ends. The clutches are made by 
binding brass or copper plates, as shown in the drawing; 
they should then be screwed fast to a base-block five inches 
long, one inch and a half wide, and five-eighths of an inch 
thick. The opening between them should just admit the 
copper ends of the fuse, and pressure should be used to force 
the fuse in place so that the contact will be perfect. 

Still another form of fuse is shown in Fig. 24. This last 
may more properly be called a non-sparking fuse, for the 
lead wire is encased in a glass tube, and when it fuses no 
sparks fly and no small pieces of melted metal can get away 
from the inside of the tube. The plug is made from a piece 
of glass tube half an inch in diameter, two metal caps, and 
a short piece of lead wire. The metal caps are of thin 
sheet-copper, and are caught at the edges with solder. One 
end of the lead fuse-wire is passed through a hole in the 
end of a cap and soldered, as shown at A in Fig. 24. The 
wire is then passed through the tube and the cap placed 
over one end of it. This is repeated at the other end and 

SO 



PUSH-BUTTONS AND SWITCHES 

the wire soldered fast. As a result, you will have a glass 
tube with metal caps held on the ends of the tube, by means 
of the thin lead wire which nms through the middle of the 
tube. The base-block to which this fuse-plug is attached 
is of wood one inch and a half wide, five or six inches long, 
and five-eighths of an inch thick. Two metal straps are 
made and screwed fast to the block, and the circuit wires 
are attached imder the copper burrs and held down by the 
screw-eyes. 

To place or replace a fuse-plug, unscrew the eyes and raise 
each strap slightly, so that the copper cap ends will pass 
under them. A turn or two of the eyes will clamp the plug 
in position and at the same time bind the circuit wires. 

A spring lightning-arrester is shown in Fig. 25; it is 
simply a modified form of that shown and described in Fig. 
19. The base-block is five by one-and-a-quarter by five- 
eighths of an inch, and is properly protected by a sheet of 
mica or asbestos. The two metal plates are cut for the 
binding-posts and screwed in place with screws, burrs, and 
screw-eyes. From spring-brass wire bend a hook and slip 
one end of it under the screw-head at the left side of the 
block. From a longer piece of wire make two or three 
turns aroimd a piece of wood half an inch in diameter ; then 
form a hook at one end and a turn at the other, so that it 
can be made fast under the screw-head of the binding-post. 
When at rest, the spring-hook should stand in an upright 
position, but when sprung and tied it occupies the position 
shown in the drawing. The spring-hook is to be bent down 
so that the two hooks are brought within an inch of each 
other. They are held in this position with a piece of lead 

51 



ELECTRICITY BOOK FOR BOYS _ 

fuse-wire. This last is given a turn about the hooks and 
one or two turns about itself, close to each hook, to prevent 
the spring from tearing itself away. When the wire is fused 
by a current the spring-hook flies up and away from possible 
contact with the short hook attached to the opposite bind- 
ing-post. This is the construction for a single-pole-spring 
lightning-arrester; a double one is made in a similar man- 
ner, and the parts mounted on a wider block, as shown in 
Fig. 20. 

For doubtful currents, where there is no means of know- 
ing how strong they are, a combined fuse and single-pole 
switch is shown in Fig. 26. This is nothing more than a 
combination of the apparatus shown in Fig. 21, and the 
single-pole switch (Fig. 10). The base block is seven inches 
long and two inches wide. Or it may be made half an inch 
wider if it is to be bevelled at the top, as shown in the draw- 
ing. It should be three-quarters of an inch thick and pro- 
vided with two countersimk holes for screws that will hold 
it in place on a ledge or against a casement. The little 
angles to hold the copper-ended mica fuse-plate are de- 
scribed for the apparatus pictured in Fig. 21. If it is desired 
that one of the ends should be provided with bvirrs and a 
screw-eye, the little plate of brass should be an inch long and 
an inch wide, with a half-inch-square piece snipped from 
one comer, as shown at A in Fig. 26. It is provided with 
two holes, and then bent on the dotted line, so that the part 
with the holes will lie on the block and the ear will stand in 
a vertical position. A reverse-plate made on this pattern 
will act as one side of the switch-bar clutch at the opposite 
end of the block. For the metal clutch and keeper at the 

52 



PUSH-BUTTONS AND SWITCHES 

middle of the block the metal plate (before it is bent) will 
appear as shown at B in Fig. 26. The long plate with two 
holes lies on the base, while the first ear (or the one without 
the hole) forms part of the clutch for the fuse end, the ear 
with the hole acting as one side of the bar-lever strap. An 
opposite plate to this forms the other side of the clutch and 
strap, and the two plates are screwed side by side, so that 
the fuse-plate will be held securely when pushed into place. 
For the switch-bar use a piece of hard copper or brass 
four inches long, half an inch wide, and about one-eighth of 
an inch thick, or the same thickness as the copper straps at 
the ends of the mica fuse-plate. Bore a hole at one end of 
this bar, and with a copper rivet attach it between the two 
upright ears at the middle of the block. With a file cut 
away the two edges at the other end of the bar for a distance 
of- an inch, so that the bar will have an end as shown at C 
in Fig. 26. Drive a small file-handle on this end and give 
it a coat or two of shellac; then bevel the lower edges of 
the bar with a file where it enters between the blades of the 
clutch. The circuit wires are made fast at both ends of the 
block, and the current travels through the binding-posts, 
the lead fuse- wire on the mica plate D, and the switch-bar. 
If the current is too strong, then when the switch-bar is 
pushed into the clutch the safety-fuse will bum out and 
save the apparatus; or it will arrest a flash of lightning. 



Chapter IV 

MAGNETS AND INDUCTION-COILS 

Simple and Horseshoe Magnets 

EVERY boy has a horseshoe magnet among his collection 
of useful odds and ends, and whether it is a large or 
small one its working principle is the same. If large enough 
it will lift a jack-knife, nails, or solid weights, such as a 
small flat-iron or an iron padlock. A horseshoe magnet is 
made of highly tempered steel and magnetized so that one 
end is a north pole and the other a south pole. In more 
scientific language these poles are known as, respectively, 
positive and negative. Once magnetized the instrument 
retains that property indefinitely, unless the power is drawn 
from it by exposure to intense heat, and even then, by suc- 
cessive heating and cooling, the magnetism may be partial- 
ly restored. 

An electro-magnet may be made of any scrap of soft 
iron, from a piece of ordinary telegraph-wire to a gigantic 
iron shaft. When a current of electricity passes through a 
wire a magnetic "field" is produced around the wire, and 
if the latter is insulated with a covering and coiled about a 
soft iron object, such as a nail, a bolt, or a rod, that object 
becomes a magnet so long as a current of electricity is pass- 

54 



MAGNETS AND INDUCTION-COILS 

ing through the coils of wire or helix. A coil of wire in the 
form of a- spiral spring has a stronger field than a straight 
wire carrying the same current, for each turn or convolution 
adds its magnetic field to that of the other turns. 

A simple form of electro-magnet is made by winding 
several layers of No. 20 insulated copper wire around a 
stout nail or a carriage-bolt; by connecting the ends to a 
battery of sufficient power, some very heavy objects may 
be lifted. A single magnet, like the one shown in Fig. i, 
is made with a piece of soft iron rod six inches long and 
half an inch in diameter, the ends of a large spool sawed off 
and worked on the rod, and half a pound of No. 20 insulated 
copper wire. The spool - ends are arranged as shown in 
Fig. 2. An end of the wire is passed through a hole in one 
flange when you begin to wind the coils, and when finished, 
the other end is passed through a hole at the outer rim of the 
same fiange. This magnet may be held in the hands when 
in use; or a hand-magnet may be constructed of a longer 
piece of iron on one end of which a handle is driven and 
held in place with a nut and washer, as shown in Fig. 3. 
The wires from the coil pass through holes made in the 
handle and come out at the butt end, where they may be 
attached by connectors to the pole-wires of a battery. To 
protect the outer insulated coil of wire from chafing and a 
possible short-circuit, it would be well to wrap several 
thicknesses of stout paper around the coil and glue it fast; 
or a leather cover will answer as well. 

A more powerful magnet may be made from a stout bolt, 
two nuts, and a wooden base, with about three-quarters of 
a pound of No. 18 insulated copper wire to wind about the 

55 



. rii ,. 




SIMPLE AND HORSESHOE MAGNETS 

56 



MAGNETS AND INDUCTION-COILS 

body of the bolt. A block of wood an inch thick, four 
inches wide, and six inches long is provided with a hole at 
the middle for the bolt to pass through. A larger hole is 
made at the under side of the block so that a nut can be 
easily turned in it. A three-quarter -inch machine-bolt, 
with a square head, and seven inches long, is set in the 
block, head up, as shown in Fig. 4 ; and composition or thin 
wooden disks or washers are placed on the bolt to hold the 
coils of wire in place. The ends of the wire pass out through 
the bottom washer and are made fast to binding-posts on 
the block, and to these latter the battery-poles are made 
fast when the magnet is in use. Coils of wire may be wound 
on an ordinary spool, and the hole in the middle may be 
filled with lengths of soft iron wire. When a current is 
passing around the spool the wires become highly magnetic, 
but lose the magnetism directly the current ceases. 

Horseshoe electro-magnets are made by winding coils on 
the ends of U-shaped pieces of soft iron, but the winding 
must be done so that the current will pass around them in 
opposite directions, otherwise you would have two nega- 
tives instead of a negative and positive. For a small 
horseshoe magnet a stout iron staple may be used, but for 
the larger magnets it would be best to have a blacksmith 
bend a piece of round iron in the desired shape. 

A powerful horseshoe magnet may be made from a piece 
of tire-iron bent as shown in Fig. 5 A; when wound with 
No. 18 wire it will appear like Fig. 5 B. A volt or two of 
current passing through the coils will render this magnet 
powerful enough to lift several pounds. 

For bells, telegraph- sounders, and other electrical equip- 

57 



ELECTRICITY BOOK FOR BOYS 

merit requiring the horseshoe or double magnet, several 
kinds may be used, but the simplest is constructed from 
two carriage or machine bolts and a yoke of soft iron, as 
shown in Fig. 6. The yoke is five-eighths of an inch in 
width, two inches and a half long, and provided with two 
three-eighths-inch_ holes, one inch and a half apart from 
centre to centre. Two-inch carriage or machine bolts are 
used, and they should be three-eighths of an inch in diam- 
eter. The nuts are turned on the thread far enough to 
admit the yoke, and then another nut is applied to hold it 
in place and bind the three pieces into one compact mass. 
Wooden spool-ends or composition washers are placed on 
the bolts to hold the ends of the wire coils in place, and 
the winding may be done on each bolt separately and 
locked to the yoke after the winding is completed. Double 
cotton-insulated No. 20 or 22 copper wire should be used 
for the coils. 

It is a tedious and bothersome job to wind a coil by hand, 
and if possible a winder should be employed for this pur- 
pose. Several varieties of winders are on the market, but 
a simple one for ordinary spools may be made from a stick 
held in an upright piece of wood with staples. This idea is 
pictured in Fig. 7, where the round stick is shown cut with 
two grooves into which the staples fit. One end of the stick 
is made with a square shoulder, so that a handle and crank 
can be fitted to it. A few wraps of wire are taken around 
the crank to prevent it from splitting, and it is held to the 
round stick with a slim steel nail. The opposite end of the 
round stick is shaved off so that it will fit snugly in the hole 
of a spool; if it should be too small for some spools, a few 

58 



MAGNETS AND INDUCTION-COILS 

turns of cord around the small end will make it bind. The 
block to which the shaft and crank is attached may be held 
in a vise or screwed to the edge of a table. 

Indtfction-coils 

A simple induction or shocking coil may be made of a 
two-and-one-half by five-sixteenths-inch bolt, a thin wooden 
spool, and two sizes of insulated copper wire. An induction- 
coil is a peculiar and wonderful apparatus ; . it figures largely 
in electrical experimenting and is a part of every complete 
equipment. 

A piece of curtain-pole may be used for the spool. First 
bore a five-sixteenths-inch hole through the wood to receive 
the bolt ; then in a lathe turn it down into a spool with less 
than one-eighth of an inch of wood about the hole and with 
flanges about one-eighth of an inch in thickness. Smooth 
the spool with sand-paper, while it is still in the lathe, and 
give it a thin coat or two of shellac. 

Slip the spool on the winder (Fig. 7) and wind on three 
layers of No. 24 cotton-insulated copper wire, taking care 
to wrap the coils evenly and close. Bring six inches of the 
ends out at either end of the spool through small holes 
pierced in the flanges; then wrap several thicknesses of 
brown paper around the coil. A current passing around 
this three-layer coil will magnetize the bolt. This is the 
primary coil and the one through which the battery current 
will pass. 

A secondary coil is now made over the primary one with 
eleven or thirteen layers of No. 30 insulated copper wire. 

59 



ELECTRICITY BOOK FOR BOYS 

It will take some time to carefully put on these layers, and 
when doing so mark down each layer so as to keep an accu- 
rate count, for there must be the right number of layers to 
make the coil act properly. No. 30 wire is quite fine, and 
if the layers are not inclined to lie smooth, make a wrap or 
two of brown paper between each three layers. Bring six 
inches of each end of the wire out from the flanges of the 
spool, and to protect the outer coil wrap paper about the 
coils and attach it fast with thread or paraffine. Slip the 
bolt through the hole and screw the nut on the threaded 
end. Cut out a wooden block four inches long, three inches 
wide, and three-quarters of an inch thick, and with two thin 
metal straps and screws attach the coil to the middle of the 
block, as shown in Fig. 8. Make four binding-posts and 
screw them fast at the corners, and to A and B of Fig. 8 
attach the ends of the heavy wire from the primary coil, 
and to C and D of Fig. 8 the ends of the fine wire from the 
secondary coils. The induction-coil is now ready for any 
use to which it may be put, and by mounting it on the block 
with the delicate wire ends attached to the binding-posts, 
it is in less danger of damage than if the wire ends were left 
loose for rough-and-ready connections. 

In order to get a shock from this coil it will be necessary 
to have a pair of handles and a current interrupter. The 
handles may be made from two pieces of tin rolled into the 
form of cylinders to which wdres are soldered. Or, better 
yet, use pieces of thin brass tubing an inch in diameter. 
The buzzer shown in Fig. 9 may be employed for a current 
interrupter, and a bichromate battery will furnish the cur- 
rent. 

60 



MAGNETS AND INDUCTION-COILS 

In order to make the connections, the wires from the 
handles are attached to the binding-posts C and D in Fig. 8 
— that is, to the wires of the secondary coil. One spool of 
the battery is connected with A of Fig. 8 and the other 
with A of Fig. 9. A wire connects C of Fig. 9 with B of Fig. 8, 
and the circuit is closed. The buzzer now begins to vibrate, 
and any one holding the handles will receive a shock the 
intensity of which depends on the strength of the batteries. 
A switch should be introduced somewhere in the circuit, so 
that it may be opened or closed at will ; a good place for it 
is between a battery-pole and the binding-post A in Fig. 8. 

If the shock is too intense it may be weakened by draw- 
ing the carbon and zinc poles partly out of the bichromate 
solution ; or a regulator may be made of a large glass tube 
and a glass preserving- jar filled with water. If the tube 
cannot be had, an Argand gas-burner chimney will answer 
as well. 

Solder a wire to the edge of a small tin or copper disk, as 
shown in Fig. 10, on which the chimney rests at the bottom 
of the jar, and another wire to a tin box-cover with some 
small holes punched in its top, this latter being suspended 
within the chimney. This second wire is passed out through 
a cork at the top of the chimney made of a disk of card- 
board and a piece of wood. One wire is connected with A 
of Fig. 8 and the other with a battery-pole. This apparatus 
acts the same as a resistance-coil, and by raising or lowering 
the box-cover the current is increased or diminished. The 
closer the cover comes to the disk the stronger the current, 
as there is less water for the electricity to pass through and 
therefore less resistance ; while if the cover touches the disk 

6i 



ELECTRICITY BOOK FOR BOYS 

the current flows as freely as if there were no regulator and 
the wires ran directly to the cell. 

An apparatus comprising a coil, an interrupter, or arma- 
ture, and a switch may be set on one block, and the arrange- 




ment of the several parts is clearly shown in the drawing of 
the complete galvano-f aradic apparatus (Fig. 1 1 ) . The block 
should be six inches long, four inches wide, and seven-eighths 
of an inch in thickness. 

The coil is made as described for Fig. 8, the spool being 
three inches long and one inch and a quarter in diameter. 
A carriage-bolt three inches and a half long and five-six- 

62 



MAGNETS AND INDUCTION-COILS 

teenths of an inch in diameter, with a bevelled head, is made 
fast in the spool, and this coil is strapped to the block 
with two metal bands and screws. Two binding-posts (A 
and B of Fig. ii) are arranged at the upper corners, and to 
these the ends of the secondary coil wires are attached. 
Two more binding-posts (C and D of Fig. ii) are arranged 
at the lower side and provided with a switch to open and 
close the circuit. One of the primary coil wires is made 
fast to C, and the other one to a block which contains the- 
set-screw that bears against the vibrating armature. Its 
arrangement and the wire connection is explained in Fig. 

9B. 

An armature of thin brass or tin is made and attached 
to a block (E in Fig. 11). At the loose end that is opposite 
the bolt-head several wraps of tin are made and soldered 
fast, or a small block of soft iron may be riveted to the 
armature. It must be of iron or tin, however, so as to be 
attracted by the electro-magnetized bolt -head. This ar- 
rangement may be seen in Fig. 12. Attach a thick piece 
of paper over the bolt-head, so that the lug at the end of the 
armature will not adhere to it through residual magnetism. 

In regular galvano-f aradic machines the current regulator 
is formed of a hollow cylinder which is drawn from the core 
of the coil; but in this simple machine the water- jar regu- 
lator may be connected between a pole of the battery and 
the binding-posts (D or E of Fig. 11). The wires of the 
handles are attached to posts (A and B of Fig. 11), and when 
all the wires are in place and the current turned on by 
means of the switch, the vibrator begins to work and the 
shocking- current is felt through the handles. By means of 

63 



ELECTRICITY BOOK FORy BOYS 

the regulating-screw that bears on the armature, the num- 
ber of vibrations may be increased or diminished, but for 
faradic purposes the vibrations should be as quick as possi- 
ble. Much amusement may be had with this apparatus, 
and a large number of people may be given a shock by get- 
ting them to join hands when standing or sitting in a circle. 

An Electric Buzzer 

This piece of apparatus is, in theory, nothing more than 
the electric bell, and might properly be included in Chapter 
v., on Annunciators and Bells. But since it is the logical 
development of principles just laid down, it has been thought 
best to give it its present position. 

The electric buzzer is constructed on the principle of the 
telegraph-sounder, but instead of making a single click or 
stroke the current is made to act on the armature and keep 
up a continuous motion so long as the electricity passes 
through the helix of the cores, the armature, and the con- 
tact-points of the apparatus. 

A buzzer has the same movement as an electric bell with 
the ringing apparatus removed. For offices, houses, and 
quiet calls it is often preferred to the loud ringing of a 
bell. 

The electric buzzer shown in Fig. 13 is easy to make; it 
is operated by the aid of a cell and a push-button. Cut a 
base-block three inches and a half wide, five inches long, 
and three-quarters of an inch thick, and mount a horseshoe 
magnet made of bolts and a yoke and coils about at the 
middle of it, as shown in Fig. 9. The magnet is held to the 

64 



MAGNETS AND INDUCTION-COILS 



base by a fiat wooden cleat and a screw passed down through 
a hole in the cleat and into the base, between the coils. An 
armature of soft iron, two inches long and half an inch wide, 
is riveted to a piece of spring-brass, as shown in Fig. 14 A, 
and the end is bent so that it will fit around the corner of a 
block to which it is held fast with two screws. This arma- 
ture is mounted so that there is a space one-sixteenth of an 
inch wide between it and the bolt-heads, as you can see 
in Fig. 9. The brass is bent out slightly and runs parallel 
with the armature for one inch and a quarter. Against this 
the end of the screw mounted in block B Fig. 9 rests. 

The block B is a small piece of hard- wood screwed fast to 
the side of the base to hold the set-screw and also the wire 




that comes from the outside of the upper coil. A small hole 
is made in the edge of the block and the wire passed in, so 
that the end rests in the screw-hole as shown by the dotted 
line. When the screw is placed in the hole and turned, it 
comes into contact with the wire and makes a connection. 
This block and its attachment is shown in Fig. 14 B. 

On the base, near the armature-block, a binding-post is 

65 



ELECTRICITY BOOK FOR BOYS 

made fast, and the current, passing in through the wire A 
in Fig. 9, goes through the coils and around to the screw B, 
then through the armature to the block, and out through 
the wire C. In its circuit the bolts are magnetized, and they 
draw the armature, but the instant they do so the loose 
spring-brass end is pulled away from the screw-point B and 
the circuit is broken, the bolts cease to be magnetized, and 
the armature flies back under the influence of the spring- 
brass neck at D. The loose brass end, on touching the 
screw-point, conducts the current through the coils again, 
with a continual vibrating action, so long as the electric 
current is passing in at A and out at C. The greater the vol- 
ume of current the greater the number of vibrations, and to 
properly regulate the contact the set-screw B must be ad- 
justed at the right point. Paste pieces of heavy paper over 
the heads of the bolts to overcome residual magnetism. 

A single electric bell is made the same as a buzzer, but 
continuing on from the end of the armature a wire or rod is 
mounted with a ball at the end which strikes the bell as the 
current causes the armature to vibrate. The bell-block 
may be made longer, and a bell from an old clock or a bicycle 
should be mounted at the proper place on a wooden dowel 
driven into the base. A screw passes through the hole at 
the middle of the bell and into the top of the dowel. The 
ball at the end of the rod may be made of brass with a hole 
in it, and a drop of solder will hold it in place. Or it may 
be made of wire wound round the end and soldered into a 
compact mass. 



MAGNETS AND INDUCTION-COILS 

A Large Indtiction-coil 

As has been said, the induction-coil is one of the myste- 
rious phenomena of electrical science. While its practical 
value is known and recognized in all branches of voltaic 
electricity for use in transforming currents, its actual work- 
ings have never been clearly explained. 

The construction of a small induction-coil was explained 
in the description of a shocker or medical battery. For 
bigger equipments, wireless telegraphy and other uses, a 
large induction-coil will be necessary, and the following 
illustrations and descriptions should enable the young elec- 
trician to construct an apparatus that will be both simple 
and efficient in its working. 

For the tube (in which to wind the primary coils) obtain 
a piece of red fibre-tubing, one inch inside diameter and not 
more than one-eighth of an inch in thickness. The length 
should be ten inches. If fibre cannot be had use a paste- 
board tube. 

From w^hite-wood, half an inch in thickness, saw two 
blocks four inches square and in the centre of each cut a 
hole so that the tube will pass through it and fit snugly. 
Some shellac and a few slim brass escutcheon pins will hold 
the blocks in place, as shown at Fig. 15. The wood blocks 
and fibre or paper tube should be treated to several suc- 
cessive coats of shellac to give them a good finish and pre- 
vent the absorption of moisture. Four binding-posts, with 
wood screw-ends, are to be made fast at the top edges of 
the end-blocks, as shown at Fig. 15. Holes bored in the 
blocks near the foot of the binding - posts will admit the 

67 



ELECTRICITY BOOK FOR BOYS 



ends of the coil- wires so that contact can be made. The 
ends of the conductor- wires should then be placed in the 
holes in the binding-posts and held in place with the thumb- 
screws. 

The primary coil is made by winding four layers of No. 





20 insulated copper wire on the tube and between the end- 
blocks, as shown at Fig. i6. Each layer must be wound 
evenly, and the strands should lie close to each other. 
When the first layer is on give it a coat of shellac; then 
wrap a piece of thin paper about it and give that also a coat 
of shellac. When the second layer is on repeat the opera- 
tion of shellacking and paper-coating, and continue with the 
third layer. When the fourth layer is on give the coil a 
double wrap of paper and two or three coats of shellac to 
thoroughly insulate it and keep out all moisture. The 
winding may be done by hand, but it is much easier to do it 
on a winder or reel, which can be operated to revolve the 
core, the wire unwinding from its original spool as it is 
wound on the tube. 
A convenient winder may be made on a base-board 

68 



MAGNETS AND INDUCTION-COILS 

which can be clamped to a table or bench. The board is 
twelve inches long, eight or ten inches wide, and seven- 
eighths of an inch thick. Two uprights, three inches wide, 
ten inches long, and three-quarters of an inch thick, are 
screwed and glued to the ends of the base-board. A notch 
is cut in the top of the end-boards, into which the spindle 
or shaft can rest ; and at the top of the end - pieces two 
small plates of wood or metal are screwed down to hold 
the spindle in place when the tube and ends are being 
revolved. A small hole, bored in each upright end two 
inches above the top of the base-board, will admit a rod on 
which a spool of wire can revolve, as shown at Fig. 17.. 

Two plugs of wood, shaped like corks, are made to fit in 
the ends of the fibre-tube. A hole is bored through each 
one so that a wire or rod spindle will pass through them 
and fit tightly. One end of the rod is bent and provided 
with a small wooden handle, by means of which the core 
may be revolved. 

This winding-rack makes it easy to handle the core-tube 
while putting on the layers of wire, and it holds the tube 
securely while the wraps of paper and shellac are applied. 

The secondary coil is laid over the primary, and should 
be of Nos. 30 to 36 insulated copper wire. The finer the 
wire the higher the resistance and the longer the spark, but 
nothing heavier than No. 30 should be used. 

Begin by making one end of the wire fast to a binding- 
post; then turn the core-tube with one hand, holding the 
wire in the other. Take care not to bind the wire nor 
stretch it, but wind it on smoothly and evenly, like the 
coils of thread on a new spool of cotton or silk. Be very 

69 



ELECTRICITY BOOK FOR BOY S 

careful to avoid kinks, breaks, or uninsulated places in the 
wire. Should the wire become broken, give the coil a coat 
of shellac to bind the wound strands; then make a fine 
twisted point and cover it with the silk or cotton covering, 
with a coat of shellac to hold it in place, and proceed with 
the winding. Between each layer of wire place a thin sheet 
of paper and coat it with paraffine, or shellac, to make a 
perfect insulation ; then proceed with the next layer. 

With a battery and small bell test the wire layers occa- 
sionally to see that everything is all right, and that there 
are no breaks or short circuits. This is very necessary to 
avoid making mistakes, and, considering the time and care 
spent in winding the coils, it would be a great disappoint- 
ment if the coil were defective. 




About one pound and a half of wire should constitute 
the secondary coil, and, if possible, it is best to have it in 
one continuous strand, without splices. 

Over the last coil, after the winding is completed, several 
thicknesses of paper should be laid and well coated with 

70 



MAGNETS AND INDUCTION-COILS 

shellac between each wrap. This is a protector to insure 
the fine wire strands from damage. To improve the ap- 
pearance of the coil a wrap of thin black or colored leather 
may be glued fast, with the seam or point at the under 
side. 

The ends of the wires forming the primary coil should 
be made fast to the binding-posts at one end, while those 
of the secondary coil should be attached to the posts at 
the other end. 

For the core, obtain some soft iron wire, about No. i8, 
and cut a number of lengths. Straighten these short wires 
and fill the tube with them, packing it closely, so that the 
wires will remain in place under a mutual pressure. It is 
better to make a core of a number of rods or wires rather 
than to have it of one solid piece of soft iron. 

Now, from hard- wood, cut a base three-quarters of an 
inch thick, five or six inches wide, and twelve inches long. 
Attach the coil to the base by means of screws passed up 
through the board and into the lower edges of the end- 
blocks. The wood is to be stained and given several suc- 
cessive coats of shellac. 

Now connect the wires of a battery to the binding-posts 
in contact with the primary coil, and attach two separate 
wires to the secondary coil binding-posts. Bring these ends 
near to each other, and a spark will leap across from one 
end to the other, its size or "fatness" depending on the 
strength of the battery. The completed apparatus is shown 
at Fig. 1 8. 

In producing a long spark a condenser is an important 
factor; it is used in series with an induction-coil. There 

71 



ELECTRICITY BOOK FOR BOYS 

are several forms of condensers, but perhaps the simplest 
and most efficient is the Fizeau condenser, which is made 
up of layers of tin-foil with paraffined paper as separators. 

From a florist's supply-house purchase one hundred and 
fifty sheets of tin-foil seven by nine inches, or sheets that 
will cut to that size without waste; also ten or twelve 
extra sheets for strips. At a paper supply-house obtain 
some clear, thin, tough paper about the thickness of good 
writing-paper. Be careful to reject any sheets that are per- 
forated or have any fine holes in them. The sheets should 
be eight by ten inches, or half an inch larger all around 
than those of the tin-foil. The paper must be thoroughly 
soaked in hot paraffine to make it moisture-proof and a 
perfect non-conductor. This is done by placing about two 
hundred sheets on the bottom of a clean tin tray, or photo- 
graphic developing-dish of porcelain. Don't use glass or 
rubber. After placing some lumps of paraffine on the 
paper, put the tray in an oven so as to dissolve the paraffine 
and thoroughly soak the paper. 

Open the oven door and, with a pin, raise up the sheets 
one at a time, and draw them out of the liquid paraffine. 
As soon as it comes in contact with cool air the paraffine 
solidifies and the sheet of paper becomes stiffened. Select 
each sheet with care, so that those employed for the con- 
denser are free from holes or imperfect places. 

From pine or white- wood, a quarter of an inch in thick- 
ness, cut two boards, eight by ten inches, and give them 
several good coats of shellac. 

To build up the condenser, lay one board on a table and 
on it place two sheets of paraffined paper. On this lay a 

72 



MAGNETS AND INDUCTION-COILS 

sheet of tin-foil, arranging it so that half an inch of paper 
will be visible around the margin. From the odd sheets 
of tin-foil cut some strips, one inch in width and three inches 
long. Place one of these strips at the left end of the first 
sheet of foil, as shown at Fig. 19. Over this lay a sheet of 
the paraffined paper, then another sheet of the foil. Now 
on this second sheet of foil lay the short strip to the right 
end, and so proceed until all the foil and paper is in place, 
arranging each alternate short strip at the opposite end. 
Care must be taken to observe this order if the condenser 
is to be of any use. 

When the last piece of foil is laid on, with its short strip 
above it, add two or three thicknesses of paper, and then 



ri<^i9 





the other board. With four screw-clamps, one at each 
corner, press together the mass of foil, paper, and boards as 
closely as possible, then bind the boards about with adhe- 
sive tape, or stout twine, and release the clamps. Attach 
all the projecting ends of foil at one side by means of a 
binding-post, and those at the other end with another 
binding-post. The complete condenser will then appear 
as shown in Fig. 20. 

When in operation one wire leading from the secondary 
coil should be connected with a binding-post of the con- 
denser, so that it is in series. 

73 



ELECTRICITY BOOK FOR BOYS 

The object of the condenser is to increase the efficiency 
of induction, and it should be made in proportion to the size 
of the induction-coil with which it is to be employed. 



Circttit-Intcrrtjpters 

When an induction-coil is to be employed as a shocker 
(and there is no vibrating armature arranged in connection 
with the core), a circuit-interrupter must be employed to 
get the effect of the pulsations, as given out by the secondary 
coil when a current is passing through the primary. 

There are various forms of circuit-breakers that may be 
made for this purpose, but for really efficient service the type 
shown in Fig. 21 is perhaps the best that can be devised. 

This interrupter consists of a metal cog-wheel with saw- 
teeth, a pinion or axle, and a handle. Also a base-block, 
with uprights to support it, and a piece of spring-brass wire, 
arranged so as to bear against the wheel. When the wheel 
is revolved the spring- wire will be driven out by each tooth ; 
and when released it flies back to the wheel, striking the 
bevelled edge of a tooth at each trip. 

Two binding-posts, arranged on the block, will provide 
means of connecting in-and-out wires. With a coat or two 
of shellac on the wood- work and black asphaltum varnish 
on all surfaces of the metal that are not used for contact, 
this circuit-interrupter will be ready for any use in connec- 
tion with an induction-coil. 

The base-block is of pine, white- wood, or cypress, se^.^en- 
eighths of an inch thick, three inches wide, and five inches 
long. The uprights, which support the wheel, are half an 

74 



MAGNETS AND INDUCTION-COILS 



inch thick and one inch wide. The wheel is three inches in 
diameter and is made of brass one-sixteenth of an inch thick. 
The design of the wheel should be laid out with a compass 
and marked with lead-pencil or a sharp-pointed awl, which 
will leave a mark clear enough to be seen when sawing and 
filing the teeth and open places. 

A true plan is shown at Fig. 21 A. Through the middle 
of the wheel a small hole is bored to receive the axle of 
brass which is to be soldered in place. When the wheel is 
set up, a metal crank and wooden handle should be soldered 
fast to one end of the axle. A piece of spring-brass wire is 




fastened to the block, with a staple, and the lower end bent 
so that the screw in one binding-post will hold it in place. 
The upper end of the wire is bent in the form of an L. 
From the other binding-post, through the block and up one 
support, a wire is passed, the end of which comes into con- 
tact with the axle. The current, passing in through one 
binding-post, is carried through this wire to the axle, then 
to the wheel, and so on out through the spring- wire and 
remaining binding-post. When in action the circuit is 

75 



ELECTRICITY BOOK FOR BOYS 



constantly being broken, as the spring- wire jumps from the 
end of one tooth back to the face of the next tooth. The 
pulsations are increased or diminished by the fast or slow 
speed of the wheel, as regulated by the hand motion. The 
strength of the current is regulated by the force of the 
battery and should be controlled by a water resistance, as 
described for the medical battery, or shocking-coil. 

The interrupter, shown in Fig. 22, is built up on a block 
six inches square and seven-eighths of an inch thick. 

A circle is cut from sheet-lead and laid on the face of the 
block, through which pins, or steel- wire nails, are driven. 
The lead circle is five inches in diameter and half an inch 
in width, making the inside diameter four inches. 

The pins or nails are driven a quarter of an inch apart, 
and should be properly and accurately separated, so that 
an even make-and-break will be the result. 

It is not necessary to bore holes in the lead, but the pins 
or nails should be driven clear through it, so that perfect 
contact can be had by the metal parts coming together. 
Otherwise the apparatus would be useless. 

Over the circle of pins a brass bridge is erected, so that 
the cross-strips will clear the heads of the pins. A hole is 
bored at the middle of the bridge so that the revolving axle 
will pass through it. 

The axle is made from a piece of stout wire, or light rod, 
and near the foot of it, and about half an inch above the 
base-board, a disk of metal is soldered fast. A piece of 
spring-brass wire is attached to this disk, so that when the 
axle is turned the end of the wire trips from pin to pin, thus 
making and breaking the circuit. The upper part of the 

76 



MAGNETS AND INDUCTION-COILS 

axle is bent and provided with a small wooden or porcelain 
knob. 

One wire from the secondary coil is caught under a screw 
that holds one end of the brass bridge to the base; -and the 
other to a screw, which may be placed at one corner of the 
block, and from which a short wire leads to the lead ring. 
Binding-posts may be arranged to serve the same purpose, 
and, of course, they are much better than the screws, be- 
cause they can be easily operated by the fingers and do not 
require a screw-driver every time the interrupter is placed 
in series with an induction-coil. An interrupter on this 
same order may be made from a straight strip of lead with 
the pins driven through the middle of it. One wire from 
the secondary coil is made fast to the lead plate, and the 
end of the other wire is passed along the pins, thus making 
and breaking the circuit in a primitive manner. 



Chapter V 

ANNUNCIATORS AND BELLS 

A Drtim Sounder 

A UNIQUE electric sounder that is sure to attract atten- 
tion is in the shape of an electric-bell apparatus, with 
a drum sounder in place of a bell, or knockerless buzzer. 
Fig. I. 

The outfit is mounted on a block four inches and a half 
wide and seven inches long. The cores and yoke are made 
as described for the electric buzzer (chapter iv.) and are 
wound with No. 22 cotton-insulated wire. The magnet is 
then strapped fast to the block by means of a hard-wood 
plate having a screw passed down through it ; and between 
the coils and into the block an armature is made and 
mounted on a metal plate, which in turn is screwed to the 
block. Another block, with a contact-point, is arranged 
to interrupt the armature, and the series is connected as 
show^n in the drawing Fig. i . 

The end of the wire projecting above the armature is pro- 
vided with a hard-wood knocker which operates upon the 
head of the drum. The drum is made from a small tin can, 
having one or two small holes punched in the bottom. Over 
the top a thin membrane, such as a bladder or a piece of 

78 



ANNUNCIATORS AND BELLS 

sheep-skin or cat-skin, is drawn and lashed fast with several 
wraps of wire, having the ends twisted together securely. 
The membrane must be wet when drawn over the can end, 
and great care should be taken to get it tight and even. 
Then, when it dries, it will stretch and draw, like a drum- 
head, and hold its elastic, resonant surface so long as it does 
not become moistened or wet. 

This drum is arranged in the proper position and lashed 
fast with wires passed over the box and down through holes 
in the block; where, after several turns, the ends may be 
securely twisted together. In place of the drum a small 
wooden box may be lashed fast with its open end against 
the block, so as to form a hollow enclosure. The raps of 
the knocker against its sides will give forth a resonant 
xylophone tone. 

An Annunciator 

A simple annunciator may be made from a core, a helix, 
and some brass strips. A soft iron core, made of a piece of 
three-eighth-inch round iron and threaded at one end, is 
converted into a magnet by having a spool and wire coil 
arranged to enclose it. This in turn is screwed into a strip 
of brass bored and threaded to receive it. Fig. 2. 

This brass strip is shaped as shown at Fig. 3 A, and the 
ears are bent to serve their several purposes. The lowest 
ears are turned out and the lower part of the plate is bent 
forward so as to form the hinge on which the drop-bar turns. 
The drop-bar is only a strip of metal turned up at one end, 
on which a numeral or letter can be attached ; while at the 
other the metal should be bent over so as to form a core into 

79 



ELECTRICITY BOOK FOR BOYS 

which a pin or wire may be passed and the extending ends 
bent down, after being caught through the holes in the ears. 
Above the magnet the strip is bent forward and the top or 
end ears bent up, so as to form the hinge on which the 
armature swings. Holes are made in the long ears, through 
which screws pass to hold the annunciator fast to the box 
or wood-work. 

The armature is made from a strip of brass and is shaped 
like B in Fig. 3. The two ears at the top are bent down 
and fit within those at the top of the first strip. A screw 
or wire passed through the holes in the ears will complete 
the hinge. The strip is bent down so as to fall in front of 
the magnet, and to its inner side a button or disk of sheet- 
iron is riveted fast, so as to form an attraction-plate to be 
drawn against the magnet when the current is passing 
around it. The lower part of the armature is bent in hook 
fashion so as to hold up the drop-bar. 

A slot is cut in the drop-bar through which the hooked 
end will project. A short spring is arranged at the top of 
the annunciator so as to keep the bar and the hook in place 
when not in action. The current passing around the soft 
iron core magnetizes it and draws the iron button on the 
armature towards it. This action immediately releases the 
hook from under the edge of the metal at the forward end 
of the slot, and the bar drops, bringing the figure down and 
into plain sight. It is necessary, of course, to mount this 
annunciator so that the bar will not drop down too far. 
This may be done by having a platform or wire run 
along under a series of the drops, so that they will rest 
on it. 

80 




5y TiG.e 



ANNUNCIATORS AND BELLS 
8l 



ELECTRICITY BOOK FOR BO Y S 

A Doable Electric Bell 

For loud ringing, and to get the benefit of both the for- 
ward and backward stroke of the knocker, a double bell, 
similar to the one shown in Fig. 4, may be constructed upon 
the general principle of the single-stroke buzzer already de- 
scribed (chapter iv.). 

Two soft iron cores are made, as described for the other 
bells, but instead of being yoked together with iron, so that 
the three parts will form a horseshoe magnet, the yoke is of 
brass or copper. Each core will then be an independent 
magnet. 

The spools are w^ound with No. 22 insulated wire and the 
ends left free, so that the coils are not connected together. 
If the drawing is examined closely you will see that the 
armature swings on a pivot at the base of the knocker-bar. 
When the bell is not in action the knocker might rest natu- 
rally against one bell or the other; or it might stand in the 
centre and not touch a contact-point, were it not for the 
small spring which draws it to the left. Directly the cur- 
rent is run through the coils it alternately magnetizes first 
one and then the other. This action is due to the making 
and breaking of the circuit by the spring on the armature. 
It .first comes into contact with one point, and then is drawn 
away from it to come into contact with the other. Fig. 4 
shows the knocker-bar at rest between both bells and the 
armature unattracted by either magnet. This position is 
purposely given so as to indicate the balance of the armature 
and the spaces between it and the cores and also the contact- 
points above it. 

82 



ANNUNCIATORS AND BELLS 

The small, light wire spring shown in the drawing draws 
the knocker to one side ; therefore, when at rest, one circuit 
is closed. Otherwise the bell would not act when the cur- 
rent is run through the parts — in fact, the current could not 
run through at all, if one or the other contact were not made. 

The magnets are held fast to a base with a long screw and 
a small plate of wood laid across them as shown in Fig. 4. 
The armature is a piece of soft iron one-eighth of an inch 
thick, half an inch wide, and three inches long. This has a 
spring-brass piece attached to it as shown at A A in Fig. 5 . 
Small holes are bored through the strip and the iron, and 
escutcheon pins are passed through and riveted. A small 
hole is made down through the middle of the iron plate and 
a pin is driven into it, so that a quarter of an inch projects 
at both sides. 

Another hole is made through the side of the plate for 
the knocker-bar. Then the armature is set in place so that 
there is a space of one-eighth of an inch between it and the 
magnet ends. The armature is held in place at the top by 
a bent metal strip (B B in Fig. 5). This is screwed fast to 
the base and the bottom is countersunk into the wood. 

Two contact-points (C C in Fig. 5) are arranged so that 
when a magnet draws the armature down it brings the 
opposite end of the armature spring into contact with a 
point. 

The wiring is at the under side of the base and is shown 
in Fig. 6. The current enters binding-post A, and passes 
around coil and magnet No. i by entering at B and leaving 
at C; from thence to D, entering the armature spring at E, 
when the small spring has drawn the knocker-bar over to 

83 



ELECTRICITY BOOK FOR BOYS 

the left. The current passes along the armature and out at 
F ; then along to binding-post G, and so on around through 
battery K and push-button L, thus completing the circuit. 
Directly that this is done the magnet draws the spring end 
of the armature away from contact-point D and up against 
contact-point J, so that the circuit is broken through coil 
No. I and is sent through coil No. 2. This immediately 
magnetizes core No. 2 and draws the armature down to it, 
breaking its contact with J and re-establishing it with D. 
The rapid alternate making and breaking of the circuit, and 
the rapid and strong motion of the armature in its seesaw- 
action, causes the knocker to rap the bells soundly each time 
it travels from right to left and back again. 

Two bells of similar size, or two drums or wooden boxes, 
may be employed for this double striker, and the more cur- 
rent that is run through the coils the more power and a cor- 
responding increase of noise. 

An Electric Horn 

One of the most useful pieces of apparatus where a loud 
noise is required (such as in a motor-boat or an automobile) 
is the electric horn. 

It is a rearranged principle of the telephone, for instead 
of sound entering or striking against the membrane or 
tympanum to be transmitted elsewhere, the disturbance 
takes place within the horn and the sound is emitted. 

Everybody has been close to a telephone when others 
have been using it, and has heard noises, rasping sounds, 
and even the voice of the speaker at the other end of the 

84 



ANNUNCIATORS AND BELLS 

line. If a cornet were played at the other end of the line 
it could be distinctly heard through the receiver by many 
persons in the room, since its vibrations are loud enough 
to set up a forcible succession of sound-waves. 

The same principle operates in the electric horn, but 
instead of being agitated at a long distance it is done within 
the enclosure, and a very much louder vibration is conse- 
quently produced. 

It is quite as easy to make an electric horn as to construct 
a bell, but care must be exercised to have the parts fit 
accurately and the wiring properly done. If the drawings 
are studied and the description closely followed, there is no 
reason why a horn cannot be made that will demand any 
one's attention from some distance away. 

The complete horn is shown in the illustration Fig. 7, 
and as it is made of wood it is easily attached with screws 
to a boat or a motor-car. 

^om white- wood, half an inch thick, cut two blocks three 
inches and a quarter square. In one of them (the rear one) 
bore a hole at the centre, of such size that a piece of three- 
eighth-inch gas-pipe can be screwed into it. In the other 
one make a hole two inches in diameter, so that the cover 
of a small tin can will fit into it. Outside this hole, and on 
one side of the block, cut the wood away and down for one- 
eighth of an inch, forming a rabbet, as shown at A in Fig. 7. 
This will be the back of the front block. 

Have a gas or steam fitter cut a piece of two-inch iron 
pipe one inch and three-quarters long. This will measure 
a trifle over two inches and a quarter, outside diameter, and 
will form the cylinder or cover for the mechanism. The 

85 




AN ELECTRIC HORN 



ANNUNCIATORS AND BELLS 

piece of pipe should fit snugly in the front board, and at 
the rear one the wood should be cut away so as to let it in 
an eighth of an inch, as shown in. the sectional plan of 
Fig. 7. 

Obtain a piece of three-eighth-inch gas-pipe, threaded at 
one end. Cut it with a hack-saw, and file the .blunt end so 
that it will measure one inch and seven-eighths long, as 
shown at C in Fig. 7. This is to be screwed into the front 
of the rear block so that it will project one inch and a half. 

Make a spool to fit the pipe, as shown at B in Fig. 7, or 
use two wooden button-moulds attached to the pipe with 
shellac or glue. Between them wind on the coils of No. 22 
wire to form the helix. 

Cut a hole in the tin-can cover, as shown at D in Fig. 7, 
and have a tinsmith solder a small funnel to it (for the horn, 
or bell, as it is called), cutting away the lower part of the 
funnel so that the hole in it will correspond in size with 
that in the can cover. 

This joint can be made at home by fitting the funnel in 
the hole and then turning back the edge, as shown in the 
sectional drawing at E in Fig. 7. Then, with a spirit-lamp, 
some soldering solution, and solder, make a good joint. 

Small holes are to be made at the corners of the blocks, 
through which stove-bolts two inches and a half long will 
fit to bind the front, back, and cylinder together. 

Select a good, clean, and fiat piece of tin and cut a disk 
two inches and a quarter in diameter, and through the mid- 
dle make a vSmall hole. Cut two pieces of iron about the 
size and thickness of a cent, and bore a small hole through 
the centre of each. Obtain a piece of stout brass wire, or 

87 



ELECTRICITY BOOK FOR BOYS 

thin rod, and file one end of it as shown at G in Fig. 7, so 
that the small end will fit in the holes made in the iron 
buttons. Place one button on either side of the tin disk, and 
pass the wire through ; then clamp it in a vise and rivet the 
top of the rod so that you will have a disk with a button at 
each side of the centre and all attached firmly to a brass 
rod, as shown at F in Fig. 7. The total length of this rod 
should be two inches and a half, and the lower end is to be 
threaded and provided with two small brass nuts. A piece 
of spring-brass three-eighths or half an inch wide is made 
fast to a small block at the back of the horn, as shown at H 
in Fig. 7, and at its opposite end a contact-piece of metal, 
bent at an a,ngle, is screwed fast. Around the back of the 
back block a wooden frame is attached to protect the rear 
mechanism of the horn. 

The parts are now ready to assemble. First see that the 
metal angle contact-point is in place with the long brass 
strip resting on it, and that this in turn is properly fastened 
to the block on the side opposite the contact-point, as shown 
at H in Fig. 7. There should be a small hole through the 
middle of the brass strip directly in line with the mid- 
dle of the hole in the gas-pipe. Place this back-board 
down on the table so that it will lie in a position as indicated 
in the sectional plan of Fig. 7. The gas-pipe is then to be 
screwed onto the plate. Over this the spool with its layers 
of wire is to be slipped and made fast, and the cylinder of 
iron is then placed in position. Over this the disk F is laid, 
so that the brass rod extends down through the pipe and 
brass strip; then the nut is screwed on to hold it in place. 
Next comes the front block, with its horn or bell, and the 

88- 



ANNUNCIATORS AND BELLS 

entire mass is locked together by means of the four bolts at 
the corners. 

The wiring is simple. One inlet being through block I, 
the current passes through strip J to contact-point K ; then 
through the coil and out at wire L. The inlet and outlet 
wires are connected to a battery and to a push-button or 
switch, so that the horn can be operated. The proper ad- 
justment of this horn depends on the nuts at the foot of the 
brass rod. They must be screwed on tight enough to draw 
the strip J so that it rests on the contact-point K. 
• The current, passing in at I, through J, K, the coil, and 
out at L, magnetizes the piece of pipe and draws the iron 
buttons or disks attached to the tin disk. But so soon as 
it does so it breaks the contact between J and K, and the 
buttons fly back into place, having been drawn there by the 
rigidity of the tin disk to which they are attached. Again 
the current is closed and the magnet draws the iron buttons. 
The brass rod moves but a very slight distance up and down 
— enough, however, to make and break the contact between 
J and K. As a result of this rapid movement and the con- 
sequent snapping of the tin disk, a loud noise is emitted 
through the bell, which can be heard a long distance and 
closely resembles a long blast blown on a fish-horn, 

B«rglar-alarms 

A unique burglar-alarm trap may be made from a plate 
of wood, five by six inches and half an inch thick, a mova- 
ble lever, and a brass strip having the ends turned out. 
These are arranged as shown in Fig. 8. The brass strip is 



ELECTRICITY BOOK FOR BOYS 

fastened to the plate with screws, and the ends extend out 
for half an inch from the board. The lever is made from a 
strip of brass, and the upper part is bent out so as to clear 
the strip and screws that are under it. A hole is made at 
the lower end of the lever, through which a brass ring and 
the end of a spring may be fastened. The opposite end of 
the spring is attached to a screw, and a wire carried from it 
to a binding-post, A. Another wire connects the back plate 
with binding-post B. A string or piece of fine picture- Vvdre 
is made fast to the ring and carried to any part of a room. 

To set the trap, make the block fast in any convenient 
place, such as the door-casing or the surbase, and carry the 
string out from the trap and fasten the end of it. Any one 
running against it in the dark will draw the lever over to 
the right side and connect the circuit. 

When setting the trap, have the string adjusted so that 
the lever is in a vertical position, as shown in the drawing 
of Fig. 8. When the string is disturbed it will pull the top 




90 



_^ ANNUNCIATORS AND BELLS 

of the lever over to the right side ; but if the string is broken 
by the person running against it, the spring attached to the 
bottom of the lever draws it over to the right side with a 
snap, and the top of the lever goes to the left side, when the 
circuit is closed and the alarm given. 

This trap is connected the same as a push-button, one 
wire leading to the bell, the other to the battery ; then the 
battery and bell are connected together so that when the 
circuit is closed the bell will ring until some one throws a 
switch open to break it. 

Another form of circuit-closer is shown in the door-trap 
(Fig. 9) . This is a wooden block that rests on the floor close 
to the bottom of a door, and is held in place by means of 
four sharp-pointed nails driven down through the corners 
of the block. The points should project a quarter of an 
inch or more, according to whether the block is on a hard 
floor or on a carpet. The front edge of the block is " bev- 
elled so that the bottom of a door that fits closely to the 
floor will pass over it. 

The block is five by seven inches, and three-quarters of an 
inch thick. At the left side a strip of metal (A) is held close 
to the block with straps or wide staples driven over it, but 
not so close but that it can move freely back and forth. To 
the front end a round piece of wood is made fast. This is 
the bumper against which the door will strike when opened. 
At the middle of the strip a screw is riveted fast ; or it may 
be a machine-screw let into a threaded hole in the metal. 
At the right side of the block another strip of metal (B) is 
attached, but this is held fast with a screw at the middle 
and a screw-eye and washer at the rear end to act as a bind- 

91 



ELECTRICITY BOOK FOR BOYS 

ing-post. The front end of this strip is turned up so as to 
form a stop ; then a movable lever (C) mounted over both 
strips, with one end bent up, is attached to the block with a 
screw. A slot is cut at one end so that the screw in the 
movable strip (A) will move freely in it, and near the other 
end a small hole is made to receive the end of a spiral spring 
(D) . To set the trap, the block is placed on the floor and 
the wires from battery and bell are made fast to the bind- 
ing-posts. The spring D keeps the lever C away from the 
strip-end B, while at the same time it throws the strip A 
forward. When the door is opened it shoves the bimiper 
and strip A back through the staples, while the screw oper- 
ates lever C and causes its loose end to come into contact 
with the end B, thereby closing the circuit and ringing the 
bell or buzzer. When the door is closed again the spring 
draws lever C away from B, and the circuit is opened. 

The block acts as an obstruction as well as an alarm, for 
the pins will hold in the floor and the little block will stand 
its ground. A simple form of contact for doors is shown 
at Fig. lo. This is simply two strips of spring-brass bent 
as shown, and screwed fast on either side the crack of a 
door, at the hinge side, so that when the door is opened 
one piece of metal bears on the other and the circuit is 
closed. This is to be operated in connection with a switch, 
so that the circuit may be opened in the daytime when the 
door is in use. 

Signals and Alarms 

There are many different kinds of electric call -signals 
used in and about the house ; among these are some that a 

92 



ANNUNCIATORS AND BELLS 

boy can readily make — for example, the ordinary call- 
buttons and the signals between house and stable or other 
out-buildings. 

A portable call-bell, or alarm, is one of the most con- 
venient things in any home. It may be temporarily rigged 
up from one room to another, or from one floor to the next, 
the small, flexible wire being run over the tops of door- 
casings, where it is held by slim nails or pins driven into 
the wood" work. 

The main terminal of this portable outfit consists of a 
-wooden box that will hold a large dry-cell, and to the side of 
which an electric bell or buzzer may be attached. Binding- 
posts are arranged at another side, to which the ends of the 
flexible wire-cord can be made fast, and a cover fitted to the 
box to hide the battery and wiring. The complete outfit, 
except the flexible wire-cord and push-button, will appear 
as shown in Fig. 1 1 . No definite size can be laid down for 
the construction of this box, as dry-cells vary in size and 
shape, some being long and thin, while others are short and 
fat. By removing the cover and looking into the box, it 
will appear as shown in Fig. 12. The carbon is connected 
with one binding-post and the zinc to one of the poles of 
the bell. The other bell-pole is connected with the remain- 
ing binding-post, and it requires but a switch or push-button 
to close the circuit between the two binding-posts. This is 
done by the long line of flexible wire-cord, which may be of 
the silk or cotton covered kind, having the two strands 
twisted together as is customary with flexible electric-light 
wire. A pear-shaped push-button may be connected at 
the end of the line, and this may be arranged at the head 

93 



ELECTRICITY BOOK FOR BOYS 

of a bed or on a chair placed conveniently near an invalid's 
couch. 

This same apparatus is a very convenient thing for a 
lecturer where a stereopticon is used. A buzzer takes the 
place of the bell, which would be too loud in a hall or 
lecture-room, and the cord, passing from the apparatus 
close to the operator, is hung over the lecturer's stand, or 
the button held by him in the hand, to be pressed whenever 
he desires the pictures changed. 

This apparatus can be used also in connection with an 
alarm-clock, where the winding-key is exposed at the back, 




as it is in most of the nickel-cased clocks that are operated 
by a spring and which have to be wound each day. For this 
purpose obtain a piece of hard rubber or fibre, one-sixteenth 

94 



ANNUNCIATORS AND BELLS 

of an inch thick, an inch long, and half an inch wide. A 
piece of stout card-board or a thin piece of hard- wood soaked 
in hot paraffine will answer just as well, if the fibre or rubber 
cannot be had. Bore a small hole at the two upper corners 
and one at the middle near the lower edge. Obtain three 
garter-clips, with springs, and rivet one of them fast to the 
little plate of non-conducting material. Cut two lengths of 
old brass watch-chain, four inches long, . or obtain eight 
inches of chain at a hardware - store, and divide it in 
half. Attach a garter - clip to one end of each piece, and 
make the other end fast in the holes at the corners of 
the small plate as shown in Fig. 13. This will be the con- 
nector and will close the circuit when the alarm goes 
off. 

When the clock is wound and the alarm-spring is tight, 
catch one binding -post with a clip at the end of a chain 
and the other post with the remaining clip. Place the clock 
near the box and grasp the alarm-key with the clip on the 
plate. When the alarm goes off the bell on the clock will 
begin to ring, and when the key has m.ade one revolution it 
twists the two pieces of chain together, closes the circuit, 
and the electric bell rings until some one unfastens one of 
the clips on the binding-posts and breaks the circuit. The 
great advantage in this double-alarm outfit is that it keeps 
the bell ringing until the attention of the sleeper is attracted. 
The bell on the clock will stop ringing directly the spring 
is unwound or run down; but in so doing it twists the 
chain and sets the electric mechanism in motion, to run 
until it is stopped, or until the battery polarizes or is ex- 
hausted. 

95 



ELECTRICITY BOOK FOR BOYS 

A Dining-table Call 

One of the most convenient of house electric-calls is that 
between the dining-room and the butler's .pantry or the 
kitchen, its purpose being to summon the waitress without 
the necessity of ringing a bell at the table, or calling. 

There are various forms of push-buttons for this purpose 
— some embedded in the floor, others hanging from the 
centre light, and others again where the wire runs up from 
under the table, and the pear-shaped push rests on the cloth 
within easy reach. These last are good enough in their way, 
but are inconvenient, unsightly, and quite liable to get out 
of order. 

In order to use the floor-push the table must stand in 
exactly the right place; with the drop-string from a chan- 
delier the cord is continually getting in the way ; and as for 
the portable push that comes from under the table, one 
must be forever hunting for the button every time the table 
is set. And yet it is quite possible to avoid all these troubles 
and construct an apparatus that is always in order and 
always available, wherever the table may be placed. A 
visitor at a certain house noticed that the number of the 
family present at a meal was apt to vary largely, necessitat- 
ing frequent lengthenings and shortenings of the table. 
And yet the waitress invariably appeared just at the right 
time, and whether one end or the other of the table was to 
be served, she was always on the spot where she was needed. 
The visitor tried to study it out, but was finally obliged to 
ask for an explanation of the mystery. The boy of the 
house smiled and intimated that he was responsible for this 

96 



ANNUNCIATORS AND BELLS 

domestic miracle; later on, when dinner was over, he 
removed the centre leaves from the table and displayed the 
simple apparatus that he had constructed and which had 
worked for several years without adjustment or repairs. 

The illustration (Fig. 14) represents the frame of a dining- 
table with the middle cross-bar made fast to the side-rails, 
so as to support the mechanism. At both ends, and inside 
the rail, push-buttons are arranged and wires carried from 
them to binding-posts close at hand, as may be seen at the 
left side. The cross-bar at the middle of the table supports 
a large spool on which the flexible cord is wound, and kept 
taut by means of a clock-spring. This spool takes up the 
slack between the ends of the table when it is lengthened 
or shortened, while the smaller one opposite it keeps taut 
the feed- wires that come up through the floor. A short 
distance from the floor the wire is provided with a connector, 
so that when the rug is removed the feed-wires may be dis- 
connected and slipped down. 

The large spool can be had at any dry-goods store where 
braids or fancy cords are kept. It should be about four 
inches long, three inches in diameter, and with sides thick 
enough to enable screws to be driven into it without fear of 
splitting the wood. An old clock-spring is attached at one 
side of the spool, while at the other two circular bands of 
brass are made fast, one within the other. An axle of stout 
wire should be driven through the spool ; but if the hole is 
too large, wooden plugs may be glued in at each end so that 
a front view of the spool will appear as shown at A. The 
metal bands are cut with shears from sheet-brass, and are 
attached with fine steel nails, the heads of which are driven 
7 97 




Fjg.h 



A DINING-TABLE CALL 



98 



ANNUNCIATORS AND BELLS 

in flush with the wood. A hole is made in the side of the 
spool, close beside each band, so that the ends of wires may 
be brought through them and attached to the bands. This 
arrangement is illustrated at B, and at C the opposite end 
is shown, with its clock-spring, one end of which is made 
fast to the side of the spool and the other to the cross-rail. 
A small round piece of wood is slipped over the axle, at the 
spring side, and projects a quarter of an inch beyond the 
spring. This is to keep the spring away from the arm that 
stands out on that side to hold the spool in place. 

About half an inch of space is left between the spool and 
the arm at the opposite side, so that the spring contact- 
strips may be made fast to the arm and still have room to 
act. A view looking down on the spool and springs is 
shown at D, and E illustrates the arrangement of the circular 
strips and the spring contact-strips. If the table is to 
remain permanently in the same position, only one spool 
will be required, for the floor wires can come up and connect 
directly with the contact-strips. But if the table is to be 
moved about, a tension-spool, independent of the push- 
button wires, is necessary so that the position of the table 
may be changed without unwinding the large spool and 
dropping the cords down to the floor. The smaller spool 
is made and mounted in the same manner, and should be 
placed close to the large one. But a lighter spring will 
operate it. One end of a double wire-cord is made fast to 
binding-posts, mounted on a yoke of hard rubber or fibre, 
so that the terminals will be kept apart, as shown at F. 
The other ends are passed through the holes at one side of 
the small spool and soldered fast to the circular strips, or 
. .^r ^ 99 



ELECTRICITY BOOK FOR BOYS 

a small screw may be passed down through the hole, binding 
the wire and touching the edge of one strip. Take care that 
it does not touch the other strip. The cord is then w^ound 
on the spool, and it is slipped in place so that the loose end 
of the spring is caught and held over a nail or screw-head. 
Turn the spool over several times to partially wind the 
spring ; then attach the terminals to the wires that come up 
from the floor and the tension of the spring will draw the 
wires taut. The two contact-strips of brass, that rest 
against the brass circles, have insulated wires leading out 
from them in order to connect them with the corresponding 
wires leading from the strips of the larger spool. 

A simple way to mount the spools is shown at A in Fig. 
15. A notch is cut in the face of the blocks large enough 
to admit the axle ; then a face-plate is screwed over the end 
of the block to hold the axle in place. This arrangement 
makes it easy to remove the spool, in case of necessity, 
without detaching the arms from the cross-rail. 

Two sets of wires are wound on the large spool, one lead- 




100 



ANNUNCIATORS AND BELLS 

ing to the right-hand and the other to the left-hand push- 
button on the table-rails. The ends of the wires are ar- 
ranged so that one leading from both directions is made 
fast to one circular strip on the spool, the other two being 
attached to the remaining band. This is more clearly 
shown at B in Fig. 15, where the ends are visible as they 
are twisted together and pass through their respective 
holes. The spool is then turned over, and six or eight feet 
of wire wound on from each side. The spring is coiled up 
and caught on the nail or screw, and the ends of the wires 
are made fast to the binding-posts near the push-buttons. 
The wires from both push-buttons are then in connection 
with the circular bands, which in turn are connected to the 
bands on the smaller spool, and lead the current down 
through the floor wires. By pushing the button at either 
end the circuit is closed and the buzzer or bell is rung in the 
kitchen or pantry. 

Arranged in this manner, the wires are kept off the floor, 
no matter where the table is moved, and it can be drawn 
open as wide as may be found necessary to put in leaves. 
When closed again, the spring causes the large spool to re- 
volve and wind up the wire. 



Chapter VI 

CURRENT-DETECTORS AND GALVANOMETERS 

A CURRENT -DETECTOR is a necessary part of the 
amateur electrician's equipment; technically, this piece 
of apparatus is called a galvanoscope. 

When a wire or a number of them are brought near a 
magnetic needle or a small compass, the needle will be 
deflected from its north and south line and will point east 
and west, or west and east, according to the direction in 
which the current is passing through the wires. All wires 
that are conducting electricity have a magnetic field, and 
when brought near the magnetized needle of a compass 
they have the power to act on it the same as another and 
stronger magnet would. 

The action of detectors depends upon two things — first, 
the magnetized needle that, when properly balanced, will 
point north and south ; and, secondly, a current of electricity 
passing through a wire or wires held above the needle, or 
both above and below it. This is more clearly shown in 
Fig. I, where a compass is resting on a wire connected to 
a battery. The wire also passes over the top of the com- 
pass, which doubles the electro-magnetic field. 

When the compass (with the needle pointing north) is 

I02 



1 



CURRENT-DETECTORS AND GALVANOMETERS 

resting on the wire that is attached to the zinc pole of a 
battery, and when the end of the wire that passes back 
over the top of the compass is attached to the carbon pole, 
the needle will fly around and point to the east. When the 
wires are reversed, the needle will point to the west. Thus 
the combination of a battery or other source of electric 
current, a magnetic needle, and a coil of wire properly 
arranged, make an instrument that will detect electric 
currents and may be correctly called a current-detector. 
The pressure of more or less current is determined by in- 
.struments wound with wire of different sizes; the finer the 
wire the more sensitive the instrument, and consequently 
the more delicate. A very weak current can only be de- 
tected with a delicate and sensitive instrument. The 
coarser the wire and the larger the instrument, the better 
it will be for testing strong currents that would perhaps 
burn out the fine wire of the more delicate apparatus. 

This instrument, when placed between a source of elec- 
tricity and a piece of apparatus, such as a bell, a motor, or 
lamp, does not weaken the current, for it requires no waste 
of electricity to operate the magnetic needle. Consequently, 
when a very weak current is being used for any tests, it is 
well to place a detector between the battery and the ap- 
paratus to show that the current is actually passing through 
the wire. 

A simple detector is made by winding fifteen or twenty 
feet of cotton-insulated copper wire No. 26 or 28 around 
the lower end of a drinking-glass. Leave six inches of each 
end loose; then after slipping the coil from the glass, tie 
the wires with thread at least four times around the circle, 

103 



ELECTRICITY BOOK FOR BOYS 

so as to bind the wires together. Press two sides of the 
hoop together so as to flatten it ; then with paraffine attach 
the coil to a square block of wood, as shown in Fig. 2. 

From a thin clock-spring, not more than three-eighths of 
an inch wide, cut a piece two inches and a half long, and 




Fig. t 



Fig. 3 




with a stout pair of tin-shears cut the ends so as to point 
them, as shown in Fig. 3 A. With two pair of pliers bend a 
hump at the middle of the strip on the dotted lines shown 
in A, so that a side-view will appear like B in Fig. 3. Turn 
this strip over on a hard- wood block or a piece of lead, and 
with a stout steel- wire nail and a hammer dent the inverted 

104 



CURRENT-DETECTORS AND GALVANOMETERS 

V at the middle so that it will rest on the top of a needle- 
point without falling off. 

With three little pieces of wood make a bridge and attach 
it to the wooden base over the paraffine that holds the wire- 
coil, and drive a needle down in the middle of it, taking 
care that it does not go through the back and touch the 
wires underneath. On this needle hang the strip of steel 
spring, and, if it does not properly balance, trim it with the 
shears or a hard file until it is adjusted properly. Rub this 
piece of steel over the pole ends of a large horseshoe mag- 
net, or place it within the helix of a large coil and turn a 
powerful current through the coil. This will magnetize the 
strip of steel, which will then become a magnetic needle and 
hold the magnetism. Attach two binding-posts to comers 
of the block, and make the loose ends of the coil- wires fast 
to them. You now have a current - detector, or galvano- 
scope, as shown in Fig. 4. Turn the block so that the needle 
points to north and south and parallel to the strands of wire. 

When the conductors from the poles of a battery or dy- 
namo are made fast to the binding-posts, the needle will 
fly around to a position at right angles to that which it first 
occupied, as shown by the dotted line A A in Fig. 4. When 
the connection is broken the needle will turn around again 
and point to north and south, since the magnetic field about 
the wire ceases and disappears the instant the circuit is 
broken. 

This is one of the strange and unknown phenomena of 
electricity, for while the current exerts a force that deflects 
the needle, it does not destroy its magnetism. On the 
breaking of the contact, no matter how long it may have 

10:: 



ELECTRICITY BOOK FOR BOYS 

held the needle away from its true course, it again points to 
north, and its magnetism is not affected. 

Another simple current-detector is shown in Fig. 5. A 
piece of broomstick is sawed in half and both pieces are 
made fast to a block which is mounted on a base of wood 
three-quarters of an inch in thickness. The vertical block 
should measure five inches long, three mches high, and five- 
eighths of an inch thick. The half-circular pieces of wood 
are mounted so that the flat surfaces are three inches apart 
and the lower edges are one inch above the base-block. 
These may be held in place with glue and screws driven 
through the back of the vertical block and into the ends 
of the projecting half -circular pieces. The base-block is 
six inches long and four inches wide, and the vertical block 
is mounted on it one inch from an edge. The pieces of 
broomstick are two inches long, and at the front ends a thin 
bar of brass or copper is screwed fast to hold them apart 
and in proper position, as shown at A in Fig. 5. To improve 
the appearance of this mounting, all the wood- work may be 
stained and shellacked before the metal parts are attached. 

With No. 26, 28, or 30 cotton-insulated wire make from 
fifteen to twenty wraps about the middle of the half-circular 
pieces of wood and carry the ends down through small holes 
in the base-block and thence through grooves cut at the 
under side of the block to the front corners, where they are 
to be made fast to binding-posts. A needle is to be set in 
the base-block midway between the two pieces of half- 
circular wood and through the strands of wire. Great care 
must be taken that the needle does not touch any bare 
wires, and as a precautionary measure it would be well to 

106 



CURRENT-DETECTORS AND GALVANOMETERS 

wrap the needle with a piece of insulating-tape where it 
passes through the strands of wire. Now place on the top 
of it a magnetized piece of steel, as described for the de- 
tector shown in Fig. 4. As it may not always be convenient 
to turn the instrument so that the needle points north, a 
small bar of magnetized steel or a stout needle that has been 
magnetized with a horseshoe magnet or a helix, may be laid 
across the half -circular wood pieces, so that it is parallel with 
the top layer of wires — in fact, it should rest on top of them.. 

By means of this needle, or bar, the magnetic piece of 
steel balanced on the vertical needle between the upper and 
lower strands of insulated wire may be held in one position 
no m^atter which way the block is turned. When the cur- 
rent passes in through one binding-post and out through 
the other (having thus travelled through the coil on the 
half-circular blocks) the needle is deflected and points out 
at the brass bar and back at the upright block. 

When making any of these pieces of apparatus, where 
delicately balanced magnetic needles are employed, all 
parts of the mounting blocks or other sections must be put 
together with glue and brass nails or screws. It will not do 
to use steel or iron nails, screw-eyes, or washers, nor pieces 
of sheet-iron, tin, or steel, for they will exert their influence 
on the vital parts of the apparatus and so destroy their use- 
fulness. This is not so important when making buzzers, 
bells, motor-induction coils, or similar things, but in delicate 
instruments, where magnetic needles or electro-magnets are 
used for recording, measuring, or detecting, iron and steel 
parts should be carefully avoided, except where their use is 
expressly indicated. 

107 



ELECTRICITY BOOK FOR BOYS 

An Astatic Current-detector ^ 

Astatic current - detectors and galvanometers are those 
having two magnetic needles arranged with the poles in. 
opposed directions. . 

The ordinary magnetic or compass needle points to the 
North, and in order to deflect it a strong magnetic field must 
be created near it. For strong electric currents the ordinary 
single-needle current-detector meets all requirements, but 
for weak currents it will be necessary to arrange a pair of 
needles, one above the other, with their poles in opposite 
directions, and placed within or near one or two coils of 
fine wire. This apparatus will be affected by the weakest 
of currents, and will indicate their presence unerringly. 

The word ''astatic" means having no magnetic directive 
tendency. If the needles of this astatic pair are separated 
and pivoted each will point to North and South, after the 
ordinary fashion. For all astatic instruments we must 
employ two magnetic needles in parallel, either side by side 
or one above another, as shown in Fig. 6, with the N and S 
poles arranged as indicated. This combination is usually 
called Nobile's pair. If both needles are of equal length 
and magnetic strength, they will be astatic, for the power 
of one counterbalances that of the other. As a consequent 
neither points to North. 

A compound needle of this form requires but a very 
feeble current to turn it one way or the other, and this is 
the theory upon which all astatic instruments are con- 
structed. 

A simple astatic current-detector may be made from a 

1 08 



CURRENT-DETECTORS AND GALVANOMETERS 

single coil of fine insulated wire, a pair of magnetic needles, 
and a support from which to suspend them, together with 
a base-block. 

For the base-block obtain a piece of white- wood, pine, 
or cypress, four inches square and three-quarters of an 
inch thick. Sand-paper it smooth, and then give it two 
or three coats of shellac. From a strip of copper or brass 
(do not use tin or iron) make a bridge, in the form of an 
inverted V, seven inches high, using metal one-sixteenth 
of an inch thick and half an inch wide. This bridge is to 
be screwed to the outside of the block, as shown at Fig. 7, 
so that it will be rigid and firm. A small hole is drilled 
through the top of the bridge to admit a screw-eye for the 
tension. 

Make a coil of No. 30 insulated wire, using ten or fifteen 
feet, and wind it about the base of a drinking-glass to 
shape it; then remove it and tie the coil, in several places, 
with cotton or silk thread, so as to hold the strands to- 
gether. Shape it in the form of an ellipse and make it fast 
to the middle of the base-board with small brass or copper 
straps, and copper tacks or brass screws. Be very careful 
not to use iron, steel, or tin about this instrument, as the 
presence of these metals would deflect the needles and 
make them useless. 

Separate the strands at the top of the coil so that one 
of the needles may be slipped through to occupy a position 
in the middle of the coil. Ordinary large compass needles 
may be employed for this apparatus, or magnetized pieces 
of highly tempered steel piano- wire will answer just as 
well. 

109 



ELECTRICITY BOOK FOR BOYS 

A short piece of brass, copper, or wood will act as the 
carrier-bar for the needles. These should be pushed through 
holes made in the bar, and held in place with a drop of shel- 
lac or melted paraffine. A small hole is drilled at the top 




of the bar, or a small eye can be attached, through which 
to pass the end of a thread. The upper end of the thread 
is tied in a screw-eye, the screw part of which passes up 
through the hole in the bridge and into a wooden button 
or knob, which can be turned to shorten or lengthen the 
thread, and so raise or lower the needles. The lower needle 



no 



CURRENT-DETECTORS AND GALVANOMETERS 

must be pivoted at an equal distance between the upper 
and lower parts of the coil. 

Two binding-posts are arranged at the corners of the 
base, and the ends of the coil wires are attached under the 
screw-heads. The in-and-out wdres are to be made fast 
under the copper washers on the screw-eyes. 

Owing to the astatic qualities of the needles, the base- 
block does not have to be turned so that the coil may face 
North and South, as in the current - detector. When the 
slightest current of electricity passes through the coil it 
instantly affects the needles, turning them to the right or 
left according to the way in which the current is running 
through the coil. 

An Astatic Galvanometer 

The sensitiveness of an astatic detector may be increased 
by the added strength of the coil-field for a given current. 

There are two ways of accomplishing this result. The 
number of turns of wire may be increased in the coil, or 
two coils may be used, placed side by side. The latter 
method is the more satisfactory, since then the coil does 
not have to be opened at the top to admit the lower needle, 
the latter being dropped down between the coils. This ap- 
paratus is shown in the illustration of an astatic galvanom- 
eter. Fig. 8. The general arrangement of needles, bridge, 
and coils is the same as described for the astatic current- 
detector. 

Each coil is made separately of ten feet of No. 30 insulated 
copper wire, wound about the base of a drinking-glass to 



ELECTRICITY BOOK FOR BOYS 

shape it; then pressed into elhptical shape, and fastened 
to a base-block with a brass or copper strip, and held down 
with small brass screws. 

The base-block should be four inches square, with the 
corners sawed off. Smooth the block with sand-paper, and 
then give it several good coats of shellac. 

The bridge is made from brass one-sixteenth of an inch 
thick and half an inch wide. The coils of wire are arranged 
about half an inch apart, and at both ends a small separator- 
block is placed between the coils, and then bound with silk 
or cotton thread. A circular indicator disk of bristol-board 
should be cut out and marked and attached to the top of 
the coils with a few drops of sealing-wax or paraffine; then 
the needles are suspended so as to hang properly, one above 
the card, the other between the coils. 

Three binding-posts are placed at one end of the block, 
and to them the end wires of the coils are led and attached. 
To the first binding-post (at the left) the strand of wire 
leading to the first coil is attached. It leads in and is coiled 
as the hands move on a clock, from left to right. The lead- 
ing-out wire from the coil is made fast to the middle post. 
The leading-in wire to the second coil is also made fast to 
the middle post, The coil wires should have the turns in 
the same direction as the first coil; then the last wire is 
attached to the right-hand post. 

When making connections for a strong current, use an 
end and middle post. This arrangement will operate but 
one coil. For very weak currents make the leading in and 
out wires fast to the end-posts. This latter plan is more 
clearly shown in the diagram. Fig. 9. A and B represent 

112 



CURRENT-DETECTORS AND GALVANOMETERS 

the coils, C, D, and E the binding-posts. The current, 
entering at C, passes through the coil A (as the hands move 
about the dial of a clock) and out at D, where connection is 
made with the wire leading in to coil B. The current passes 
through this coil in the same direction as the clock hands 
move, and out to post E. Be careful to arrange the wiring 
and connections after this exact manner, otherwise the in- 
strument will not be of any use. 

The adjustment at the top of the bridge may be made 
with an inverted screw-eye and a small cork into which the 
eye can be screwed, thus raising or lowering the needles to 
the proper position. Be sure to have the needles in parallel 
when at rest. 

As the needles and coils are very sensitive it would be 
well to cover the instrument with an inverted glass jar. 
A bluestone or gravity battery jar will answer very well, 
and after the wires are connected to the binding-posts the 
glass may be placed over the entire apparatus. 

A Tangent Galvanometer 

For testing the various degrees of intensity of a current 
a tangent galvanometer is usually employed. In this ap- 
paratus the increased strength is indicated by the index- 
pointer as it plays over a scale or graduated circle. 

A simple tangent galvanometer may be made from a fiat 
hoop of wood-fibre or brass, mounted on a base by means 
of two uprights, together with the necessary compass 
needle, an index-card, insulated wire, and binding-posts 
for the electrical connections. This piece of apparatus is 
s 113 



ELECTRICITY BOOK FOR BOYS 

shown in Fig. lo. It is built on a base-block six by seven 
inches and three-quarters of an inch thick. The block 
should be of selected wood, and after it is made smooth it 
should be given several coats of shellac. 

Two upright pieces of wood, five inches long, half an inch 
thick, and one inch in width, are screwed fast to the rear 
edges of the base-block to support the hoop on which the 
insulated wire is wound. Be careful not to use any iron or 
steel in the construction of this or any other recording 
instrument, except where it is expressly stated. Screws, 
nails, staples, or any bits of anchoring wire should be of 
copper or brass. String, thread, or silk may be used, espe- 
cially where coils of wire are to be bound or fastened to 
hoops or base-blocks. The balance of the indicating needle 
is so delicate, and the sensitiveness of the coils is so easily 
affected, that nothing about or near the instruments should 
be of iron or steel. 

The hoop may be made of very thin hickory wood, 
steamed and bent so as to form a ring six inches outside 
diameter and one inch wide. It is even possible to con- 
struct a satisfactory hoop from a ribbon of brown paper, 
rolled and lapped, the several thicknesses being glued as 
the turns are made. 

If a metal hoop is to be used, solder the ends of a thin, 
hard ribbon of brass, copper, or zinc. This strip should be 
provided with holes, set in pairs about four inches apart, 
all around the hoop, and where the hoop is to be attached 
to the uprights two holes should be made close to the 
margins through which brass screws may pass. 

Across the middle of the hoop a strip of wood six inches 

114 



CURRENT-DETECTORS AND GALVANOMETERS 

long, an inch wide, and a quarter of an inch thick is made 
fast. On this the graduated card is placed, and at the 
centre the balanced magnetic needle is arranged on a pivot. 

After the cross-stick is in place, wind five turns of No. 24 
insulated copper wire about the hoop, keeping it as nearly 
in the centre as possible. One end of the wire (the begin- 
ning) is to be attached to the first binding-post on the front 
of the base, and the other end to the second post. The wire 
should be wound round the hoop in the same direction as 
the clock hands travel about a dial. 

Another coil, comiposed of ten turns of wire, is made over 
the first one, the beginning end being attached to the mid- 
dle binding-post and the last end to the third post. This 
arrangement is shown in Fig. 11, D and E representing the 
coils, while A, B, and C are the binding-posts. The current 
enters at A, passes through coil D, and out at post B. The 
next passage is in at B, through E, and out at C. A current 
passing in at A will travel to B, thence through E, and out 
at C. If the leading-in wire is made fast to A, and the out 
wire to C, the current will travel through the entire coil. 

Under this plan one or both coils may be used (the short 
or long one as desired) by making connections with the first 
and second binding-posts, the second and third, or the first 
and third, as the strength of the current will warrant. 

Strong currents will deflect the needle when travelling 
through a short coil, but the weaker the current the more 
coils it will have to pass through to properly deflect the 
needle and indicating pointer. 

When the coils are all on, the hoop should be attached 
to the uprights with small brass screws driven through holes 

115 




^(^1"^ 




7iQ.i2 




TANGENT GALVANOMETERS 
Il6 



CURRENT-DETECTORS AND GALVANOMETERS 

in the hoop and into the wood. The wire is bound to the 
hoop by means of threads or silk passed through each pair 
of holes in the hoop, and then tied fast. Fine insulated 
wire may be used in place of the thread, but care should 
be taken that the insulation is in perfect shape on both 
the binding and coil wires; otherwise a short-circuit will 
quickly destroy the value of the coils. 

The hoop should not touch the base-block, but should 
clear it by a quarter or half an inch. Make the coil ends 
fast (as described for the astatic galvanometer and illus- 
trated at Fig. 9) by means of binding-posts. The wires need 
not be carried over the top of the block, but may run through 
holes under the hoop and along grooves cut in the under side 
of the block and leading to the foot of the binding-posts. 

The graduated card should be made from a piece of stout 
bristol-board or heavy card-board having a smooth, hard 
surface. It is laid out with a pencil or pen compass, as 
shown at Fig. 12, and should be three inches in diameter. 
The card is placed on the wood strip or ledge, so that the 
zero marks will be at the front and rear, or at right angles 
to the hoop and coils of wire. The compass needle, when 
at rest, should lie parallel with the coils, so that the current 
will deflect the needle and send the indicator around to one 
side or the other of zero, according to the direction in which 
the current is passing through the coils. 

This is more clearly shown at Fig. 13. The circle repre- 
sents the outside diameter of the card ; the dark cross-piece, 
the magnetic needle; and the pointed indicator, a stiff 
paper, or very thin brass or copper strip, cut and attached 
to the needle with shellac or paraffine. 

117 



ELECTRICITY BOOK FOR BOYS 

When at rest the magnetic needle should be parallel to 
the coils. To insure this the instrument must be moved 
so that the lines of wire forming the coil will run North and 
South. Otherwise the N-seeking end of the magnetic shaft 
will point to North, irrespective of the position occupied by 
the wire coil. 

The magnetic needle may be made as described for the 
compass (see chapter iv., Magnets and Induction Coils). 
It should be arranged to rest on a brass pivot pressed down 
into the cross-piece of wood. 

The indicator-needle may be cut from stiff paper, thin 
sheet-fibre, or very thin cold-rolled brass or copper, the 
latter being commonly known as hard or spring-brass. 
Only one pointer is really necessary — ^that pointing to the 
front. But the weight of the material would have a ten- 
dency to upset the magnetic needle, and therefore it is better 
to carry an equally long tail or end, on the opposite side, to 
properly balance the needle. 

A very weak current, passing in through the first post 
and out at the third, will cause the indicator to be deflected 
considerably, or so that it will point from 40° to 60° on 
either side of the zero point, according to the direction in 
which the current is running through the coils. 

When not in use the magnetic needle should be removed 
from the pivot, and placed in a box or other safe place, 
where it will not become damaged. 

A differently arranged tangent galvanometer is shown at 
Fig. 14. As the line of binding-posts would indicate, there 
are several coils of wire about the circle or hoop. 

This galvanometer can be used for either strong or weak 

118 



CURRENT-DETECTORS AND GALVANOMETERS 

currents, since it is wound with both coarse and fine insu- 
lated wire. An upright plate of wood, seven inches wide 
and eight inches high, supports the hoop and compass. 
The top corners are sawed off, and four inches above the 
bottom a straight cut is made across the plate, five inches 
wide and arched in a half - circle five inches in diameter. 
A shelf of wood a quarter of an inch thick, three inches 
wide, and five inches long is made, and attached as a ledge 
in this arched opening, so that a compass three inches in 
diameter may rest upon it. 

. The shelf should be arranged so that it will hold the 
compass in the middle of the circle instead of at one side. 
The turns of wire will then be in line with the magnetic 
needle when the latter is at rest. A base-block seven inches 
long, three inches wide, and seven-eighths of an inch thick 
is cut and attached to the upright plate by driving screws 
through the bottom of the plate and into the rear edge of 
the base. The corners are to be cut from the front of the 
base, and ten small holes are to be bored half an inch out 
from the upright and about a quarter of an inch apart. 
These are for the end wires that will extend down from the 
coils, and from thence to the binding-post holes. Grooves 
may be cut in the under side of the base-block for the wires 
to rest, in, as shown at Fig. 15, which is a view of the in- 
verted base. 

A hoop is made of brass, six inches in diameter and an 
inch wide. It is held to the upright plate with copper wire 
passed through a small hole, bored at the inner edge of the 
band, and back through two small holes bored in the plate, 
the ends being twisted together at the back of the plate. 

119 



ELECTRICITY BOOK FOR BOYS 

A wire at the top, bottom, and both sides will be sufficient 
to hold it securely in place. 

The first coil of wire is made of No. i8 insulated, and the 
beginning end is made fast to the binding-post at the left. 
The wire is carried up through the first hole under the hoop, 
and after three turns have been made the end is carried 
down through the second hole and made fast to the foot of 
the second binding-post. 

The second coil is of No. 24 insulated copper wire. The 
beginning end is made fast to the second binding-post, car- 
ried up through the third hole, given five turns about the 
hoop, drawn down through the fourth hole, and attached 
to the third binding-post. 

The third coil is of the same size wire but has ten turns. 
The fourth coil has twenty turns, and the fifth, of No. 30 
insulated wire, has thirty turns, the last end being attached 
to the post at the right. In all the coils there should be a 
total of sixty-eight turns, or about one hundred and five 
feet of wire. 

For strong currents the in-and-out wires may be attached 
to posts Nos. I and 2 at the left, and for weaker currents to 
Nos. 2 and 3. For still weaker currents, use Nos. 3 and 4, 
and so on. To detect the very weakest currents, attach 
the in-and-out wires to the first and last post, and let the 
current travel through all the coils or the entire length of 
the wire wound about the hoop. 

The magnetic needle is made in the same manner as 
described for Fig. 10, and the pointer is attached in a sim- 
ilar fashion. But instead of being mounted on a pivot 
over a card, and so exposed to the open air and possible 

120 



CURRENT-DETECTORS AND GALVANOMETERS 

draughts, the delicate mechanism is arranged within a brass 
hoop, which is made fast to the ledge. The graduated card 
is at the bottom of the hoop, or box fomied by it, and to 
protect the needle and prevent it from being displaced it 
should be covered with glass. This can be done by making 
a split ring of spring-brass wire and pressing it down inside 
the hoop. Over this a round piece of glass is placed, and 
another hoop is pressed in above it to hold the glass in 
position. If the rings are carefully made and of stout wire 
they will stay in place ; otherwise a drop of melted sealing- 
wax or paraffine will be necessary to keep them where they 
are wanted. 

The glass should be arranged close enough to the needle 
to prevent it from jumping or being shaken off the support- 
ing pin, but not so close as to prevent its moving easily. 



Part II 



Chapter VII 

ELECTRICAL RESISTANCE 

THE science of controlling forces is so well imderstood 
and figured out that it becomes a simple mechanical 
proposition to adapt the various types of controllers to any 
form of power that may be employed. The tremendous 
force stored within the mechanism of a great transatlantic 
liner is governed by the twist of a man's wrist. The 
locomotive that will pull a himdred cars loaded with coal, 
representing a weight of thousands of tons, is started and 
stopped by a short lever that is drawn in one direction or 
the other by a man's hand. Great forces of all kinds are 
quite as easily controlled as the supply of gas through a 
jet — by simply turning the key that lets out so much as 
may be required, no matter what the pressure is back of 
the flow. 

This same principle applies to electricity, but the means of 
governing it is vastly different from the methods employ- 
ed for other forces. Electricity is an unknown and unseen 
force, coming from apparently nowhere and returning to its 
undiscovered country immediately upon the completion of 
its work. The flow of steam, water, liquid air, gas, and 
compressed air through pipes is governed by a throttle or 

125 



ELECTRICITY BOOK FOR BOYS 

cock, which allows as much or as little to pass as may be 
required ; and if the joints, unions, and couplings in the pipes 
are not absolutely tight there will be a leakage. Electricity 
is controlled by resistance in its passage through solid wires, 
rods, or bars, and cannot be confined within a given space 
like water, nor held in tanks or pipes as a vapor or gas. It 
is invisible, colorless, odorless, and occupies no apparent 
space that can be measured; it is the most powerful and 
terrible and yet docile force known to man, doing his bidding 
at all times when properly governed and regulated. In 
some respects, electricity can be compared to water stored 
in a tank — for instance, if you have a tank of water contain- 
ing fifty gallons at an elevation of twenty-five feet, and a 
pipe leading down from it, the pressure of the water at the 
outlet of the pipe will be a given number of pounds. Now 
if the tank were double the size the pressure at the outlet 
of the pipe would be proportionately greater. Now if you 
have a battery made up of a number of cells they will de- 
velop a given number of volts, and if the number of the cells 
be doubled the voltage will be correspondingly increased. 
Or if you have a dynamo giving a certain number of volts, 
that number may be increased by doubling the size. 

The water contained within the tank represents its pres- 
sure at the outlet of the pipe. The current in volts, gener- 
ated in a battery or dynamo, represents its pressure on an 
outlet or conductor wire; and both represent the force be- 
hind their respective conductors. The valve, or faucet, at 
the end of the pipe plus the friction in the pipe would rep- 
resent the resistance to the flow of water, while the re- 
sistance-coils or other mediums plus the size of the wire, or 

126 



ELECTRICAL RESISTANCE 



conductor and switch, would regulate the flow of electric 

current. The flow of water in a pipe under certain pressure 
would represent its gallons per minute or hour, while with 
electricity its flow in a wire or other conductor would rep- 
resent its amperage. It is to govern the flow of current 
that resisting mediums are employed. 

The resistance of electric current is measured in ohms, and 
it is with this phase that we are interested in this chapter. 
If there is only a small resistance put in the path of a cur- 
rent, then it requires but a small pressure or voltage to send 
it through the wires or circuit. This is easily imder stood 
by the boy who has experimented with small incandescent 
lamps in which short pieces of carbon-filament are con- 
tained. It requires the pressure of a few volts only to send 
the current through the carbon; but for the large carbon- 
filaments, measuring ten or twelve inches in length, from, 
one hundred to five hundred volts may be necessary. The 
ordinary' house lamps require one hundred and ten volts 
and half an ampere to give sixteen candle-power. 

It is easil}" understood, then, that it requires a high pres- 
sure or voltage to force the current through the resisting 
carbon-filament, or across the space from one carbon to the 
other in the arc-lamps used for street Hghting. The shorter 
and larger the conducting wires the less the resistance, and 
consequently the lower the voltage or pressure necessRry to 
force it. Contrariwise the longer and finer the conducting 
wires, the greater the resistance. As copper is the best 
commercial conductor of electric currents, it is in imiversal 
use, and in it the minimum of resistance is oft'ered to the 
current. Iron wire is a poorer conductor, and is not used 



ELECTRICITY BOOK FOR BOYS 

for high voltage (such as trolleys or transmission of power) , 
but is confined to telegraph and telephone lines and low- 
pressure work. German-silver wire, one of the poorest 
conductors, is not used for lines at all, but is employed 
solely as a resisting medium for controlling current. 

Ohm's Law 

This is the fundamental formula expressing the relations 
between current, electro-motive force, and resistance in an 
active electric circuit. It may be expressed in several ways 
with the same result, as follows: 

1. The current strength is equal to the E. M. F. (electro- 
motive force) divided by the resistance. 

2. The E. M. F. (electro-motive force) is equal to the 
current strength multiplied by the resistance. 

3. The resistance is equal to the E. M. F. (electro-motive 
force) divided by the current strength. 

All these are different forms of the same statement ; and 
when figuring electrical data, C stands for current, E for 
electro -motive force, and R for resistance. 

Resistance-coils and Rheostats 

The method by which electricity is controlled is resistance. 
No matter how great the voltage of a current, nor its volume 
in amperes, it can be brought down from the deadly force 
of the electric trolley-current to the mild degree needed to 
run a small fan-motor, an electric bell, or a miniature lamp. 
This is accomplished by means of resisting mediums, such 

128 



ELECTRICAL RESISTANCE 



as fluids or wires, which hold back the current, and allow 
only the small quantity to pass that may be required to 
operate the apparatus. 

The jump from the high voltage of the trolley-current to 
the low one required for the electric bell, a lamp, or a small 
motor, is frequently made in traction- work, but in this oase 
regular transformers are used. For the small apparatus, 
that may have its current supplied from a battery, or a 
small dynamo driven by a water-motor, the forms of resist- 
ance-coils and rheostats described on the following pages 
should meet every requirement. 

The standard unit of resistance is called an ohm, so 
named after Dr. G. S. Ohm, a German electrician, whose 
theory on the subject is accepted as the basis on which to 
calculate all electrical resistance. The legal ohm is the 
resistance of a mercury column one square millimetre in 
cross-sectional area and one hundred and six centimetres in 
length, and at a temperature of o° Centigrade or 32° Fahren- 
heit, or the freezing-point for water. The conductivity of 
metals is dependent greatly on their temperature, a hot wire 
being a much better conductor than a cold one. Since 
counter-electro-motive force sometimes gives a spurious re- 
sistance, the ohmic resistance is the true standard by which 
all current is gauged. 

In technical mechanism and close readings the ohmic 
resistance counts for a great deal, but in the simple appara- 
tus that a boy can make the German-silver resistance coils 
and the liquid resistance will answer every purpose. 

To give a clearer idea of the principle of the rheostats, a 
short description of the mercurial column will first be pre- 
9 129 



ELECTRICITY BOOK FOR BOYS 



sented. During the early part of the last century wires were 
not used as a resisting medium for electric currents. In their 
place, glass tubes, filled with mercury sealed at one end and 
corked at the other, were arranged in rows and supported in 
a wooden rack. 

Wires led out from the top and bottom of each tube, 
and were brought down to metal buttons arranged in a row 
along the front edge of the base-plate, as shown in the illus- 
tration of a mercurial rheostat (Fig. i). Each tube repre- 
sented a certain resistance — one or more ohms, as required. 
The outlet wire was attached to the button at one end of the 




Fig. 1 

130 



ELECTRICAL RESISTANCE 



row, and the inlet could be moved along from button to 
button, until the required amount of current was obtained. 

The mercurial rheostat was an expensive, cumbersome, 
and treacherous thing to handle ; it was liable to break, and 
its weight often prohibited its use in places where the more 
convenient and easily handled German-silver rheostats are 
now in universal employment. Overheating the mercury in 
the columns caused it to expand, and sometimes, before the 
switch could be thrown open, an end would be forced out 
and the mercury would climb over the edge of the glass 
columns. 

All metals have a certain amount of resistance for electric 
currents, and some have more than others. German-silver, 
for instance — a metal made of a mixture of other metals with 
about eighteen per cent, of nickel (see Appendix) — is con- 
sidered to be the best commercial resistance medium, while 
pure copper is regarded as the best commercial conductor. 
Unalloyed copper is universally employed for electric con- 
ductors of high voltage; but for telegraph and telephone 
work, galvanized iron w^ire is still used extensively. 

The finer the wire, the higher is its resistance, and the more 
resistant the metal, the greater are the number of ohms to a 
given length. To nine feet and nine inches of No. 30 copper 
wire there is one ohm resistance, while to No. 24 — which is 
six sizes coarser — there is one ohm to thirty-nine feet and 
one inch. In many cases it is necessary to use the coarser 
wire and greater length, as the current would superheat or 
burn the fine wire, while the coarser would conduct it safely. 

For very high voltage and amperage — such as used in trac- 
tion cars, in power stations, and in manufacturing plants — ■ 



ELECTRICITY BOOK FOR BOYS 

castings of German-silver are employed and linked in series. 
They are more easily handled than the coils of wire, and a 
greater number of them can be accommodated in a small 
space. 

For light currents in experimental work, where batteries 
are employed, obtain a pound or two of bare German-silver 
wire, from Nos. 24 to 30, and wind the strands on a round 




Fig. 2 

piece of stick attached to a winder (see Magnets and In- 
duction -Coils, chapter iv.). Make several of these coils, 
two or three inches long, with the wire wound closely and 
evenly. When pulled apart the coils will appear as shown 
in Fig. 2 A, and will resemble a spiral spring. This can 
be made fast over a porcelain knob and the ends caught 
down, as shown at B in Fig. 2, or it may be drawn over a 

132 



ELECTRICAL RESISTANCE 



roiind stick, a porcelain tube, or a lug made of plaster of 
Paris and dextrine (three parts of the former to one of the 
latter) , as shown at C in Fig. 2 , and the ends securely bound 
with a strand or two of wire, twisted tight to keep the ends 
from slipping. 

The lugs may be made in a mold, using as a pattern a 
piece of broom-handle — shellacked and oiled to prevent the 
plaster from adhering to it. Obtain a small square and 
deep box, and drop some of the wet mixture down in the 
bottom; on this place the broomstick, small end down (it 
should be slightly tapered) , and around it pour in the wet 
plaster mixture. While it is setting, turn the stick with the 
thumb and fingers, so as to shape the hole perfectly then 
draw it out, and a true mold will be the result. When dry 
enough, pour some shellac down into the mold and re- 
volve it, so that the shellac will be evenly distributed, and 
let it harden for a day. Then saw off the end of the mold, 
so that it will be open at both ends. 

In order to make the lugs, pour in the plaster mixture, 
taking care to oil the mold before each pouring, so that 
the lug can be drawn out when the mixture has set. If it 
sticks, tap the small end gently to start it. For coils where 
there is little or no heat, ordinary pieces of broom-handle, 
or round sticks having a coat or two of shellac, will answer 
very well; but where the current heats the core, it must be 
of some material that will not char. 

Another method of making resistance-coils is to measure 
off a length of wire ; then double it, and with a small staple 
attach the loop end at one end of the (wooden) core. Pay 
out the two strands of wire an equal distance apart with the 

^^33 



ELECTRICITY BOOK FOR BO YS 

thumb and fingers, and with the other hand twist the core. 
At the other end of the spool catch the loose ends of the 
wire under small staples, taking great care not to let the 
staples touch or even be driven close together. This ar- 




rangement is shown at D in Fig. 2 , and for a field resistance- 
board any number of these coils may be made. 

In Fig. 3 the mode of connecting coils is shown. The 
dots represent contact-points to which the movable arm can 
be shifted. The wires at the bottom of coil, Nos. i and 2, 
are connected together, while those at the top of No. 2 and 

134 



ELECTRICAL RESISTANCE 



3 are joined, and so on to the end. The leading-in current 
is connected at pole H and so on to J, while the leading- 
out wire is made fast to pole I. The switch-arm is moved 
on the first dot, or contact-point, and the current passes up 
wire A, down coil No. i, up coil No. 2, down No. 3, up No. 
4, and so on to No. 6, and down wire G and out at I. Sup- 
posing that this offers too much resistance, the switch-arm 
is moved up one point. This cuts out coil No. i, as the 
current passes up wire B, through coil No. 2, down No. 3, 
and so on, and out through G and pole I. Another move 
of the switch and coil No. 2 is cut out, the current passing 
up wire C, down coil No. 3, up No. 4, and so on, and out at 
I. Each move of the switch cuts out one coil, lessening the 
resistance; but when moved to the last contact-point the 
current flows without resistance — in at H, through the 
switch-arm, and out at I. 

The plan of arranging the coils suggested at Fig. 2 B is 
shown in Fig. 4, where four of the coils are arranged in series 
over porcelain knobs, and the lower ends made fast to the 
base-board with small staples. Small pieces of brass are 
used for the switch contact-plates ; those are provided with 
one plain and one countersunk hole for a flat and round 
headed screw. 

The screw-heads are arranged in a semicircular fashion, 
so that the switch-arm, attached at one end to the screw J, 
will touch each plate as it is moved forward or backward. 

The current passing in at binding-post A travels to J and 
B, the latter being the resting-plate for the sw4tch-arm. 
A move of the arm to C sends the current up over the first 
coil and down; then over the second, third, and fourth 

135 




Fig. 4 




I 



Fig. 5 

TWO SIMPLE FORMS OF RHEOSTATS 
136 



ELECTRICAL RESISTANCE 



coils, and out at G ; through plate H (which is the rest at the 
right side), and out at L 

A move of the switch-arm to D cuts out the first coil; a 
move to E, the first and second coils; and so on until the 
last plate is reached, when the current will pass without re- 
sistance in at A, through J, and out at I. 

A simple arrangement for a resistance- coil is shown in 
Fig. 5 . This consists of a set of small metal plates in which 
two holes are made, one for a screw, the other for a screw- 
eye (see Binding-posts, chapter iii.). Two lines of steel- 
wire nails are driven along a board, and German-silver wire 
is drawn around them in zig-zag fashion, beginning at the 
left and going towards the right side of the board. One end 
of wire is made fast under the screw-head on plate A. The 
strand is carried out around the first nail on the lower row 
and over the first one on the upper row, then down, up, down 
until six nails have been turned. The wire is then carried 
down to the screw in plate B, given two turns, and carried 
up again and over the nail on the top row, repeating the 
direction of zigzag No. i, until six of them are made. The 
end of the wire is then made fast to plate G, and all the 
screws are driven in to hold the plates and wire securely. 

The inlet wire is attached to A, the outlet to G, and any 
degree of resistance can be had by moving the inlet wire to 
the various plates along the line, cutting out sections Nos. i 
to 6 as desired. 

For heavier wire the arrangement as shown in Fig. 6 
should be satisfactory. 

A frame twelve by fifteen inches is constructed of wood 
three-quarters of an inch thick and one inch and a quarter 

137 



ELECTRICITY BOOK FOR BOYS 



wide, having the ends securely fastened with gkie and 
screws. Spirals are wound of German-silver wire (any size 
from No. 1 6 to 22), and drawn apart. The ends are caught 




138 



ELECTRICAL RESISTANCE 



to the frame with small staples, and each alternate coil-end 
is joined, as shown in Fig. 6. The leading-out wires to the 
contact-points on the switch should be of insulated copper, 
and are to run down the sides of the frame, and so to the 
switch-board. To clearly illustrate, however, the plan of 
wiring, the drawing is made so as to show the leads from 
the coil-ends to the switch. Care should be taken to study 
this drawing well, so as not to make an error in connecting 
a wrong end to a contact-point, thereby causing a short 
circuit. When properly connected the current passes in at 
A and out at I; but if wires are improperly connected, the 
current will jump when the switch-arm reaches the mis- 
connected contact. 

The switch is an important part of every rheostat, and 
should be carefully and accurately made. One of the 
simplest and most practical switches is constructed from a 
short, flat bar of brass or copper having a knob attached at 
one end and a hole provided at the other through which a 
screw may pass (see Switches, chapter iii.). The contact- 
points are made from one or two copper washers, with the 
holes countersunk so that a machine screw of brass, with a 
flat head, will fit the hole snugly. The top of the head 
will then be flush with the top of the washer, as shown at 
Fig. 7 A. The bolt is passed down through a piece of board, 
then slate or soaps tone, and caught with a washer and nut, 
as shown at Fig. 7 B. A loop of wire is passed about the 
bolt end, then another nut is screwed tightly over it to hold 
it in place, as well as to lock the first nut. The binding- 
posts that hold the inlet and outlet wires may be made of 
bolts and nuts also, as shown at Fig. 7 B ; but the bolt must 

139 



ELECTRICITY BOOK FOR BOYS 

be passed through the switchboard so that the head is at 
the rear and the ends project out to receive the nuts. 

A very compact and simple rheostat and switch is shown 
in Fig. 8. It is composed of a base-board, eight blocks of 
hard- wood, and a top strip used as a binder to lock the upper 
ends of the blocks together. The hard- wood blocks are 
three-quarters of an inch thick, one inch and a half wide, and 
four inches long. A small hole is made near each end of 
the block and through one of them an end of the wire is 
passed. The wire is then wound round the block, taking 
care to lay it on evenly, and with about one-eighth of an 
inch of space between each strand. When the opposite 
hole is reached, pass the end of the wire through it and clip 
it. The block will then resemble Fig. 7 C. There should 
be three or four inches of wire at each end for convenience in 
connection, and when the eight blocks are wound they are 
to be mounted on end at the rear side of a base-board meas- 
uring ten inches long, three inches wide at the ends, and 
nine at the middle (or across the face of the switchboard 
to the rear edge behind the blocks). Use slim steel- wire 
nails and glue to attach the blocks to the base; -or slender 
screws may be employed. Across the top lay a piece of 
wood a quarter of an inch in thickness, and drive small nails 
or screws down through it and into the blocks. 

Connect the ends of the coils together in series, as al- 
ready described, and carry the wires under the base-plate in 
grooves cut with a V-shaped chisel. If the sunken wires 
are bothersome, the work may be avoided by running the 
wires direct to the foot of the contact-points and elevating 
the rheostat on four small blocks that may be screwed, or 

140 




COMPACT FORMS OF RHEOSTATS 
141 



ELECTRICITY BOOK FOR BOYS 

« ■ ■ — 

nailed and glued, under the corners, as shown in Fig. 8. 
These will raise the base half an inch or more above the 
table on which the rheostat will rest so as to allow room for 
the under wires. 

A rheostat of round blocks standing on end is shown at 
Fig. 9 A. These are pieces of curtain-pole, four inches long 
and wound with loops of No. i6 or i8 wire, as shown at 
Fig. 9 B. The loop and loose ends are caught with staples, 
and when arranged on a base-board they are to be con- 
nected in series as before described. One long, slim screw 
passed up through the base-board and into the lower end 
of the block will hold each block securely in place. To 
keep it from twisting, a little glue may be placed under the 
blocks so that when the screw draws the block down to the 
base it will stay there permanently upon the hardening of 
the glue. The leading wires should be slipped under the 
washers forming the contact-points of the switch; or they 
may be carried under the board to the nuts that hold the 
lower ends of the bolts. 

Another form of rheostat (Fig. lo A) is made by sawing 
a one-inch curtain-pole into four-inch lengths and cross- 
cutting each piece w^ith eight or ten notches, as shown at 
Fig. lo B. These pieces are screwed and glued fast along 
each side of a base-board eight inches wide and fourteen 
inches long, so that the notches face the outer edges of the 
board . The strand of wire passes round these upright blocks 
and fits into the notches so as to prevent them from falling 
down. 

The top end of wire at each pair of blocks is made fast by 
a turn or two of another piece of wire and a twist to hold it 

142 



ELECTRICAL RESISTANCE 



securely; then the loose end is carried down through a hole 
and along under the board to the foot of a contact-point. 

Any number of these upright coils may be made, and on a 
long board the switch may be arranged at one side instead 
of at the end, as shown in Fig. lo A. When making ten or 
more coils it is best to use three or four sizes of wire, begin- 
ning with fine and ending with coarse. For instance, in a 
twelve-coil rheostat make three coils of No. 26, three of No. 
22, and three of No. 18; or if coarser wire is required use 
Nos. 20, 16, and 12. 

German-silver comes bare and insulated. It is preferable 
to have the fine wire insulated, but the heavier sizes may be 
bare, as it is cheaper; moreover, if heated too much the in- 
sulation will burn or char off. When cutting out the coils 
always begin at the end where the finer wire is wound; 
then as the current is admitted more freely the heavier wires 
will conduct it without becoming overheated. 

For running a sewdng-machine, fan, or other small direct- 
current motor wound for low voltage, the house current (if 
electric lights are used in the house) may be brought down 
to the required voltage with German-silver rheostats sim- 
ilar to these already described. Another and very simple 
method is to arrange sixteen-candle-power lamps in series, 
as shown in Fig. 1 1 . Six porcelain lamp-sockets are screw- 
ed fast to a wood base and the leading in and out wires 
brought to binding-posts or the contact-points of a switch. 
The leading-in wire to the series is made fast at binding-post 
A, which in turn is connected with screw B, under the head 
of which the switch-arm is held. When the switch is thrown 
over to contact-point C the current passes through lamp 

143 



ELECTRICITY BOOK FOR BOYS 

No. I back to point D ; through lamp No. 2 back to E ; then 
through lamps Nos. 3, 4, 5, and 6, and out through point I 
to post J. A turn of the switch to D cuts out lamp No. i, to 
E cuts out No. 2, and so on. The filaments of incandescent 
lamps in their vacuum are among the very best mediums of 
resistance, and with a short series of lamps a current of 




Fig. 12 



220 volts can quickly be cut down to a few volts for light 
experimental work or to run some small piece of apparatus. 
Lamps in series are often used to cut down the current for 
operating electric toys and trains. The adjustment of the 
current should never be left to children, however, but should 
be attended to by some one qualified to look after the 
apparatus. Otherwise an unpleasant or even dangerous 

144 



ELECTRICAL RESISTANCE 



shock may be received. Another simple form of resistance 
apparatus is made from the carbon pencils used for arc 
lights. Short pieces will answer very well, but if the long 
bare ones can be had they will be found preferable. Do not 
use the copper-plated ones as they would conduct the cur- 
rent too freely ; they should be bare and black. Now around 
the ends of each piece take several turns of copper wire for 
the terminals and cut-out wires. Fasten those pencils down 
on a board (as shown at Fig. 12) by boring small holes 
through the board, passing a loop of copper wire down 
through the holes, and giving the ends a twist underneath. 
The leading wires to and from the contact-points should be 
insulated and may be above or below the board. From the 
descriptions already given, the connections of this rheostat 
can readily be understood. 

The rheostat shown in Fig. 1 3 is perhaps the most com- 
plete and practical apparatus that a boy could make or 
would need. It is composed of a frame, six porcelain tubes, 
a switchboard, and the necessary German-silver and copper 
wire. 

From an electrical supply-house obtain six porcelain tubes 
fourteen by three-quarter inch. Porcelain tubes and rods 
warp in the firing and are seldom straight; in purchasing 
these select them as nearly perfect as possible in shape, size, 
and length. 

Buy, also, twelve small porcelain knobs that are the right 
size to fit inside the large tubes. These should have holes 
bored through them to admit screws. Construct a frame 
of hard-wood to accommodate the tubes, as shown in the 
drawing, and leave one end loose. With slim screws make 
10 145 




A PANEL RHEOSTAT 
146 



ELECTRICAL RESISTANCE 



the porcelain knobs fast to the top and bottom strips of the 
frame, as shown in Fig. 14. The porcelain rods will fit over 
these and will thus be held securely in the frame, one small 
knob entering the tube at each end, as indicated by the 
dotted lines in Fig. 14. 

The first porcelain tube to the left is wound with No. 22 
German-silver wire, the next with No. 20, the third with 
No. 18, then Nos. 16, 14, and 12 ; so that in this field a broad 
range can be had for a current of no volts. 

The coils are connected in series, as explained for the other 
rheostats, and the leading wires brought down to the back 
of a switchboard of which Fig. 13 A is the front and Fig. 13 
B the rear view. The switchboard is made of thin slate or 
soapstone; or a fibre-board may be employed. Fibre-board 
is especially made for electrical work, and can be had from 
a large supply-house in pieces of various thickness, three- 
eighths of an inch being about right for this board. Brass 
bolts and nuts and copper washers are used for the contact- 
poles, and when the ends of the leading wires are looped 
around the bolts the nuts are to be screwed down tightly so 
as to make good contacts. This rheostat may be used when 
lying on a table, or it can be hung up by means of two 
screw-eyes driven in the top of the frame, as shown in 
Fig. 13 A. ^ . 

A convenient form of rheostat for fine wire and high 
resistance is shown in Fig. 15. This is on the plan of the 
well-known Wheatstone rheostat and does not require a 
switchboard nor a series of coils. Two rollers, one of wood 
the other of metal or brass-covered wood, are set in a frame, 
and by means of a handle and projecting ends with square 

147 



ELECTRICITY BOOK FOR BOYS 

shoulders, one or the other of the rollers may be turned so 
that the wire on one winds up while on the other it un- 
winds. 

The wooden roller may be made from a piece of curtain- 
rod one inch in diameter, and it should have a thread cut 
on it. This will have to be done on a screw-cutting lathe, 
and any machinist will do it for a few cents. There should 
be from twelve to sixteen threads to the inch — no more — 
although there may be as few as eight. Twelve will be 
found a good number, as that does not crowd the coils and 
the risk of their touching is minimized. The ends of the 
roller should have bearings that will lit in holes made in the 
end-pieces of the frame, and at one end of each roller a 
square shoulder is to be cut, as shown at A in Fig. i6. A 
short handle may be made from two small pieces of wood, 
as shown at B in Fig. i6. It must be provided with a square 
hole so that it will fit on the roller ends. The metal roller 
may be made from a piece of light brass tubing one inch in 
diameter through which a wooden core is slipped ; or it can 
be a piece of brass-covered curtain-pole with the ends shaped 
the same as the wooden one. The wood roller should have 
a collar of thin brass or copper (or other soft metal except 
lead) attached to the front end ; or several turns of wire may 
be made about the roller so as to. form a contact-point. A 
piece of spring brass, copper, or tin rests on this collar and 
is held fast under a binding- post, which in turn is screwed 
to the wooden frame. A similar strip of spring metal is 
held under another post on the opposite side of the frame 
and bears on the metal roller. 

German-silver wire is wound on the wooden roller, one 

148 



ELECTRICAL RESISTANCE 



end having been made fast to the metal collar ; and when all 
the thread grooves on the wood roller are filled the opposite 
end of the wire is attached to the rear end of the metal roller. 
The current entering at binding-post No. i crosses on the 
strip of spring metal to the collar, travels along the coil of 
wire, and crosses to the metal roller and is conducted out 
at binding-post No. 2 (see Fig. 15). If the resistance is too 
great slip the handle over the end of the metal roller and 
give it several turns. The current will then pass with 
greater freedom as the wire on the wooden roller becomes 
shorter. This may be readily seen by connecting a small 
lamp in series with a battery and this rheostat. As the 




ELECTRICITY BOOK FOR BOYS 

metal cylinder is turned the current flows more freely and 
the filament becomes red, then white, and finally burns to 
its full capacity. Take care, however, not to admit too 
much current as it will burn out the lamp. Some sort of 
adjustment should be made to prevent the rollers turning 
of themselves and thus allowing the wire coils to slacken. 
This may be done by boring the two holes for the rollers to 
fit in and then, with a key-hole saw, cutting the stick as 
shown at C in Fig. i6, taking care not to split it at the ends. 
The result will be a long slot which, however, has nothing to 
do with the bearings. Down through the middle of the 
stick make a hole with an awl, so that the screw-eye will 
move easily in the upper half but will hold in the lower 
half. Under the head of the eye place a small copper washer ; 
then with the thumb and finger drive the screw-eye down 
until the head rests on the washer. 

A slight turn of the eye when it is in the right place will 
draw the upper and lower parts of the stick together and 
bind the wood about the bearing ends of the rollers. The 
rollers should not be held too tightly as that would strain 
the wire when winding it from one to the other. It should 
be just tight enough to keep the wire taut. 

Two or more of these roller resistance-frames may be 
made and connected in series so that a close adjustment can 
be had when using battery currents for experimenting. 

Liquid Resistance 

Apart from metallic, mercurial, or carbon resistance a 
form of liquid apparatus is frequently used in laboratory 
and light experimental work. 

150 



ELECTRICAL RESISTANCE 



This style of resistance equipment is the least expensive 
to make, and will give excellent satisfaction to the boy who 
is using light currents for induction-coils, lamps, galvanom- 
eters, and testing in general. The simplest fonn of liquid 
resistance is made by using a glass bottle with the upper 
part cut away. The cutting may be done with a steel- 
wheel glass-cutter. The bottle should then be tapped on 
the cut line until the top part falls away. Go over the sharp 
edges with an old file to chafe the edge and round it; then 





Fig. 19 



Fig. 17 



solder a tin, copper, or brass disk to a piece of well-insulated 
wire and drop it down in the bottom of the receptacle, as 
shown at Fig. 17. Cut a smaller disk of metal, or use a 
brass button, and suspend it on a copper wire which passes 
through a small hole in a piece of wood at the top of the jar. 
Notches should be cut at the under side of this wood cross- 



ELECTRICITY BOOK FOR BOYS 

piece so that it will fit on top of the jar and stay in place. 
The jar is to be nearly filled with water, having a teaspoon- 
ful of sulphate of copper dissolved in it. This will turn the 
water a bluish color and make it a slightly better conductor, 
particularly when the button is lowered close to the round 
disk. If a high resistance is desired the copper may be 
omitted leaving the water in its pure state. The wires lead- 
ing in and out of the jar should be connected between the 
apparatus and the battery so that the proper amperage can 
be had by raising or lowering the button. A series of these 
liquid resistance- jars may be made of glass tubes an inch in 
diameter and twelve inches long. One end of them may 
be stopped with a cement made of plaster of Paris six parts, 
ground silex or fine white sand two parts, and dextrine two 
parts. Mix the ingredients together when dry, taking care 
to break all small lumps in the dextrine; then add water 
until it is of a thick consistency like soft putty. Solder the 
ends of some copper wires to disks of copper or brass and set 
them on the middle of bone-buttons ; these in turn are to be 
imbedded in the mixture after the wire has been passed 
through a hole in the bottom. 

Their location can be seen in the bottom of the tubes 
Fig. 1 8, and Fig. 19 A is an enlarged figure drawing of the 
plate, button, and wire. The wires are brought out under 
the lower edge of the tubes, and enough of the composition 
is floated about the bottom and outer edge of the tube to 
form a base, as shown in the drawing. A base -board is 
made six inches wide and long enough to accommodate the 
desired number of tubes. Two pieces of wood one inch 
wide and three-quarters of an inch thick have hollow notches 



ELECTRICAL RESISTANCE 



cut from them at one side, as shown at Fig. 19 B. In these 
notches the tubes are gripped. Screws are passed through 
one stick and into the other so as to clamp the wood and 
tubes securely together. The rear stick is supported on 
two uprights which are made fast to the rear edge of the 
base-plate with screws and glue. 

Along the front of the base-board small metal contact 
plates, or binding-posts, are arranged (see Binding-posts, 
chapter iii.) and the wires led to them from the tubes, as 
shown in the drawing. The top or drop wires in the tubes 
are provided with metal buttons at the ends ; or the end of 
the wire may be rolled up so as to form a little knob. The 
manner of connecting the wires was freely explained in the 
resistance-coil descriptions and may be studied out by 
examining the drawing closely. In this resistance-apparatus 
there are two ways of cutting out a medium — first, by lower- 
ing the wire in the tube so that both contact-points meet ; and 
second, by cutting out the first tube altogether by connect- 
ing the incoming wire with the second binding-post. Then 
again the resistance may be regulated quite accurately by 
raising or lowering the wires in the liquid. 

For example, there is too much resistance if the current 
has to travel through all the tubes. If it is too strong when 
one tube is cut out, the w4re in tube No. i is lowered so that 
the contacts are an inch apart. Then the more accurate 
adjustment is made by dropping the wire in the second tube, 
as shown in Fig. 18. The wires leading out at the top of the 
tubes are pinched over the edge to hold them in place. They 
should be cotton insulated and the part that is in the liquid 
should be coated with hot parafiine. 

^53 



ELECTRICITY BOOK FOR BOYS 

The water may be made a slightly better conductor if a 
small portion of sulphate of zinc, or sulphate of copper, is 
added to each tubeful. » 

Hittorf 's resistance- tube is one of the oldest on these lines, 
and two or more of them are coupled in series, as described 




ELECTRICAL RESISTANCE 



for this water-tube resistance ; glass tubes are employed that 
have one end sealed with a permanent composition, as de- 
scribed for Fig. 1 8. A metallic cadmium electrode is placed 
at the bottom of the tube, and the tube is then filled with 
a solution of cadmium iodide one part and amylic alcohol 
nine parts, and then corked. A wire passing down through 
or at the side of the cork is attached to another small piece 
of metallic cadmium, which touches the top of or is sus- 
pended a short distance in the liquid. 

As the alcohol is volatile the cork cannot be left out of the 
tube, and the wire must be draw^n through the cork with a 
needle so that no opening is left for evaporation. A nimiber 
of these tubes may be made and coupled in series and the 
wires led down to the contact-points of a switch. 



Chapter VIII 

THE TELEPHONE 

FOR direct communication over short or moderately 
long distances, nothing has been invented as yet that 
will take the place of the telephone. A few ^^ears ago, when 
this instrument was first brought out, it was the wonder of 
the times, just as wireless telegraphy is to-day. Starting 
with the simple form of the two cups with membranes across 
the ends, and a string or a wire connecting them, we have 
to-day the complex and wonderful electric telephone, giving 
perfect service up to a distance of two thousand miles. 
Some day inventors in the science of telephony will make it 
possible to communicate across or under the oceans, and 
when the boys of to-day grow to manhood they should be 
able to transact business by 'phone from San Francisco to 
the Far East, or from the cities near the Atlantic coast to 
London, Paris, or Berlin. 

It is hardly necessary to enter into the history of tele- 
phones, as this information may be readily found in any 
modern encyclopedia or reference work. But the boy who 
is interested in electricity wants to know how to make a 
telephone, and how to do it in the up-to-date way, with the 
wire and ground lines, switches, cut-outs, bell connections, 

156 



TELEPHONES 



and other vital parts, properly constructed and assembled. 
In this laudable ambition we will endeavor to help him. 

The general principle of the telephone may be explained 
in the statement that it is an apparatus for the conveyance 
of the human voice, or indeed any sounds which are the 
direct result of vibration. 

Sound is due to the vibrations of matter. A piano string 
produces sound because of its vibration when struck, or 
pulled to one side and then released. This vibration sets 
the air in rapid motion, and the result is the recording of 
the sound on our ear-drums, the latter corresponding to the 
film of sheepskin or bladder drawn over the hollow cup or 
cylinder of a toy telephone. When the head of a drum is 
struck with a small stick it vibrates. In this case the 
vibrations are set in motion by the blow, while in the tele- 
phone a similar phenomenon is the result of vibratory waves 
falling from the voice on the thin membrane, or disk of 
metal, in the transmitter. When these vibrations reach the 
ear-drum the nervous system, corresponding to electricity 
in the mechanical telephone, carries this sound to our brains, 
where it is recorded and understood. In the telephone the 
wire, charged with electricity, carries the sound from one 
place to another, through the agencies of magnetism and 
vibration. 

Over short distances, however, magnetism and electricity 
need not be employed for the transmission of sound. A 
short-line telephone may be built on purely vibratory prin- 
ciples. Almost every boy has made a "phone" with two 
tomato-cans over which a membrane is drawn at one end 
and tied. The middle of the membrane is punctured, and 

157 



ELECTRICITY BOOK FOR BOYS 

a button, or other small, fiat object, is arranged in connec- 
tion with the wires that lead from can to can. 



A Bladder Telephone 

A really practical talking apparatus of this simple nature 
may be made from two fresh beef bladders obtained from 
a slaughter-house or from the butcher. You will also need 
two boards with holes cut in them, two buttons, some tacks, 
and a length of fine, hard, brass, copper, or tinned iron wire. 
The size should be No. 22 or No. 24. The boards should 
be ten by fourteen inches and half an inch in thickness. 
Cut holes in them eight inches in diameter, having first 
struck a circle with a compass. This may be done with a 
keyhole saw and the edges sand-papered to remove rough 
places. Prepare the bladders by blowing them up and tie- 
ing them. Leave them inflated for a day or two until they 
have stretched, but do not let them get hard or dry. 

When the bladders are ready, cut off the necks, and also 
remove about one-third of the material, measuring from 
end to end. Soak the bladders in warm water until they 
become soft and white. Stretch them, loosely but evenly, 
over the opening in the boards, letting the inside of the 
bladder be on top, and tack them temporarily all around, 
one inch from the edge of the opening. Test for evenness 
by pushing down the bladder at the middle. If it stretches 
smoothly and without wrinkles it will do; otherwise the 
position and tacks must be changed until it sets perfectly 
smooth. 

The bladder must now be permanently fastened to the 

T58 



TELEPHONES 



board by means of a leather band half an inch wide and 
tacks driven closely, as shown in Fig. i. With a sharp 
knife trim away the rough edges of the bladder that extend 




Fig. 4 

beyond the circle of leather. • Attach a piece of the fine wire 
to a button, as shown in Fig. 2, and pass the free end 
through the centre of the bladder until the button rests on 

159 



ELECTRICITY BOOK FOR BOYS 

its surface. Then fasten an eight-pound weight to the end 
of the wire and set in the sun for a few hours, until thorough- 
ly dry, as shown at Fig. 3. 

When both drums are complete, place one at each end 
of a line, and connect the short wires with the long wire, 
drawing the latter quite taut. The course of the main wire 
should be as straight as possible, and should it be too long 
it may be supported by string loops fastened to the limbs of 
trees, or suspended from the cross-piece of supports made 
in the form of a gallows-tree or letter F. To communicate 
it will be necessary to tap on the button with a lead-pencil 
or small hard- wood stick. The vibration will be heard at 
the other end of the line and will attract attention. 

By speaking close to the bladder in a clear, distinct tone, 
the sound will carry for at least a quarter of a mile, and the 
return vibrations of the voice at the other end of the line 
can be clearly recognized. 

A Single (Receiver) Line 

The principal parts of the modern telephone apparatus 
are the transmitter, receiver, induction-coil, signal-bell, push- 
button, batteries, and switch. The boxes, wall-plates, etc., 
etc., are but accessories to which the active parts are at- 
tached. 

The first telephone that came into general use was the 
invention of Graham Bell, and the principle of his receiver 
has not been materially changed from that day to this, ex- 
cept that now a double-pole magnet and two fine wire coils 
are employed in place of the single magnet and one coil. A 

160 



TELEPHONES 



practical form of single magnet receiver that any boy can 
easily construct is shown in Fig. 4, and Fig. 5 is a sectional 
drawing of the receiver drawn as though it had been sliced 
or sawed in two, from front to rear. 

It is made from a piece of curtain-pole one inch and an 
eighth in diameter and three inches and a half long. A hole 
three-eighths of an inch in diameter is bored its entire 
length at the middle, and through this the magnet passes. 
At one end of this tube a wooden pill-box (E) is made fast 
with glue, or a wooden cup may be turned out on a lathe 
and attached to the magnet tube. If the pill-box is em- 
ployed it should be two inches and a half in diameter, and 
at four equidistant places inside the box small lugs of wood 
are to be glued fast. Into these lugs the screws employed 
to hold the cap are driven. The walls of pill-boxes are so 
thin that without these lugs the cap could not be fastened 
over the thin disk of metal (D) unless it w^ere tied or wired 
on, and that would not look well. If the cup is turned the 
walls should be left thick enough to pass the screws into, 
and the inside diameter should then be one inch and three- 
quarters. 

The cap (B) is made from thin wood, fibre, or hard rubber. 
It is provided with a thin rim or collar to separate its inner 
side from the face of the disk (D) . Four small holes are bored 
near the edge of this cap, so that the screw^s which hold it 
fast to the cup (E) may pass through them. The magnet (M) 
is a piece of hard steel three-eighths of an inch in diameter 
and four inches and a quarter long. This may be purchased 
at a supply-house, and if it is not hard enough a blacksmith, 
can make it so by heating and plunging it in cold water 
n 161 



ELECTRICITY BOOK FOR BOYS 



several times. It may be magnetized by rubbing it over 
the surface of a large horseshoe magnet, or if you live near 
a power station you can get one of the workmen to magnetize 
it for you at a trifling cost. Should you happen to possess a 
bar magnet of soft iron with a number of coils of wire, and 
also a storage-battery, the steel bar may be substituted for 
the soft iron core and the current turned on. After five 








Fig. 5 




162 



TELEPHONES 



minutes the steel can be withdrawn. It is now a magnet, 
and will hold its magnetism indefinitely. 

Now have a thin, flat spool turned from maple or box- 
wood to fit over one end of the rod, and wind it with a num^- 
ber of layers of No. 36 copper wire insulated with silk. 
This is known in the electrical supply-houses as '' phone "- 
receiver insulated wire, and will cost about fifty cents an 
ounce. One ounce will be enough for two receivers. It 
should be wound evenly and smoothly, like the strands of 
thread on a spool, and this may be done with the aid of 
the winder described on page 58. 

When the wire is in place a drop of hot paraffine will 
hold the end so that the wire will not unwind. The ends 
of this spool- winding should be made fast to heavier wires, 
which are run through small holes in the tube (A) and pro- 
ject out at the end, as shown at F F. The magnet, with its 
wire- wound spool on the end, is then pushed through the 
hole in A until the top end of the rod is slightly below the 
edges of the cup (E) , so that w^hen the metal disk (D) is laid 
over the cup (E) the space between the magnet and disk, or 
diaphragm (D), is one-sixteenth of an inch (see Fig. 5). Put 
some shellac on the magnet, so that when it is in the right 
place the shellac will dry and hold it fast. 

The cap (B) holds the disk(D) in place, and protects the 
spool and its fine wire from being damaged and from collect- 
ing dust. After giving the exterior a coat of black paint 
and a finishing coat or two of shellac, the receiver will be 
ready for use. 

The original telephone apparatus was made up of these 
receivers only — one at each end of a line in connection with 

163 



ELECTRICITY BOOK FOR BOYS 

a battery, bell, push-button, and switch. On a window- 
casing, or the wall through which the wires passed, a light- 
ning-arrester was arranged and made fast. Using receivers 
only, it was necessary to speak through the same instrument 
that one heard through, and for a few years this unhandy 
method of communication was the only one possible. Then 
the transmitter was invented. 



Plan of Installation 

Many of these single-receiver lines are still in use, and as 
they require but a small amount of constructive skill a 
diagram of the wiring and the plan of arrangement is shown 
in Fig. 6. 

At the left side, R is the receiver at one end of the line 
and R 2 that at the other, line No. i being a continuous 
wire between the two receivers. When the boy at R wishes 
to call his friend at R 2 he uses his push-button (PB), and 
the battery (B B) operates the electric bell (E B 2) at the 
other end. In order to have the bell connections operative, 
the switch (S 2) must be thrown over to the left when the 
line is " quiet," w^hile the switch (S) should be thrown to the 
right. With the switches in this position the boy at either 
end may call his friend at the opposite end. 

With the switch (S 2) thrown to the left (the position it 
should be in, except when talking over the line), the boy at 
the other end pushes his button (P B) , first throwing switch 
S to the left. This makes connection for the battery (B B) , 
and the circuit is closed through wires that join line No. i 
and line No. 2 at i and 2. The branch lines to the bell 

164 



TELEPHONES 



(E B 2) join the main lines at 3 and 4, through switch S 2, 
when the bar is thrown to the left. The circuit being com- 
plete, the batteries (B B) at one end of the line ring the bell 
(E B 2) at the other end of the line. 

In the reverse manner, when the switch (S) is thrown to 
the right, the boy at the opposite end. rings the bell (E B) 
by pressing on the button (P B 2), first throwing switch S 2 
over to the right. If the boy at the left is calling up the 
boy at the right, the switch (S) should be thrown to the left, 
and he keeps ringing until the other operator throws switch 
S 2 over to the right. If now he has the receiver (R) up to 
his ear he can hear the vibration of the bell (E B 2) ringing 
through the receiver (R) at his end of the line But when 
the boy summoned to R 2 takes up the receiver and places 
it to his ear, he throws switch S 2 over to the right side, and 
the boy at R leaves switch S over on the left side. This 
brings the lines into direct connection with the receivers in 
series. Be careful, when setting up this line, to have the 
batteries (B B) in series with B 2 B 2 ; otherwise there would 
be counter-action. The carbon of one cell should be con- 
nected with the zinc of the next cell, and so on. 

Another receiver is shown at Fig. 7. The tube (A) and 
the cup are turned from one piece of wood, and the cap (B) 
from another piece. The length of the receiver is five inches, 
and the cap is two inches and a half across. The shank, or 
handle, through which the magnet is passed measures one 
inch and a quarter in diameter. 

These wood parts will have to be made by a wood-turner; 
and before the long piece is put in a lathe the hole, three- 
eighths of an inch in diameter, should be bored. It must be 

165 



ELECTRICITY BOOK FOR BOYS 



done carefully, so that the wood shell will be of even thick- 
ness all around the hole. Also two small holes should be 
made the entire length of the handle, through which the 
wires leading from the coil to the binding - posts may 
pass. 

The spool for the fine insulated wire coil is turned from 
box- wood or maple, and wound as described in chapter iv., 




Fig. 7 



on Magnets and Induction-coils. Small binding-posts (F F) 
with screw ends should be driven down into the holes at 
the end of the handle and over the bare ends of the wires 
that project out of the holes. The magnet (M) is three- 
eighths of an inch in diameter, and is provided with the 
spool and coil (C) at the large end of the receiver. 

The disk (D) is of very thin iron, and is held in place by the 
cap (B) and four small brass screws driven through the edge 
of B and into the cup end of A. A screw-eye should be 
driven into the small end of the receiver from which it may 
If a double hook and bar is employed 
i66 



hang from a hook 



TELEPHONES 



the receiver will hang in the fork, being held there by the 
rim of wood turned at the small end of A. 



A Dotfble-pole Receiver 

Another form of receiver is shown at Fig. 8. This is a 
double-pole receiver, with the coils of fine wire arranged on 
the ends of a bent band of steel and located in the cup (A), 
so that the ends of the magnet are close to the diaphragm 
(D). Fig. 8 is a sectional view of an assembled receiver, but 




Fig. 8 

a good idea can be had from the drawings of the separate 
parts. The magnet (M) is of steel one-eighth of an inch thick 

167 



ELECTRICITY BOOK FOR BOYS 

and five-eighths of an inch wide. A blacksmith will make 
this at a small cost. It should measure two and one-half 
inches wide, two and one-half inches long, the ends being 
five-eighths of an inch apart. 

Thin wooden spools are made from wood or fibre to fit 
over the steel ends, and are wound with No. 36 silk-insulated 
wire. A wooden cup, or shell (A), is turned from cherry, 
maple, or other close-grained wood, and at the back a hole 
is cut just large enough for the magnet ends to slip through 
exclusive of the coils wound on them. A plug of wood (A A) 
is driven between the ends of the magnet to hold them in 
place. Some shellac on the edges of the hole and the plug 
will harden and keep the parts in place. 

The coils (C C) are placed on the magnet ends, and the fine 
wires are made fast to the binding-posts (E E), the latter be- 
ing screwed fast to the shell (A). The diaphragm (D) is then 
arranged in place and held with the cap (B) and the small 
screws which pass through it and into the shell (A). 

The Transmitter 

With any one of these receivers a more complete and 
convenient telephone can be made by the addition of a 
transmitter and an induction-coil. 

Following the invention of the receiver, several trans- 
mitters were designed and patented, among them being 
the Edison, Blake, Clamond, Western Union, and Hunning. 
The Edison and Hunning are the ones in general use, and 
as either of them can easily be made by a boy a simplified 
type of both is shown in P'igs. 9 and 11. 

168 




SIMPLIFIED TYPE OF TRANSMITTER 
169 



ELECTRICITY BOOK FOR BOYS 



Some small blocks of wood, tin funnels, small screws, 
granulated or powdered carbon, some thin pieces of fiat 
carbon, and a piece of very thin ferrotype plate will be the 
principal things needed in making a transmitter similar to 
the one shown in Fig. 9. All that is visible from the out- 
side is a plate of wood screwed to a block of wood, and a 
mouth-piece made fast to the thin board. 

In Fig. 10 an interior section is shown, which when once 
understood will be found extremely simple. The block (A) is 
of pine, white- wood, birch, or cherry, and is two inches and 
three-quarters square and five-eighths or three-quarters of 
an inch thick. A hole seven-eighths of an inch in diameter 
is bored in the centre of this block, half an inch deep, and 
a path is cut at the face of the block one inch and a half 
in diameter and one-eighth of an inch deep. Be careful to 
cut these holes accurately and smoothly, and if it is not 
possible to do so, it would be well to have them put in a 
lathe and turned out. 

The face-plate (B) is two inches square, w^th a three-quar- 
ter-inch hole in it, and the under-side is cut away for one- 
eighth of an inch in depth and one inch and a half in di- 
ameter. The object of these depressions in block A and 
face-plate B is to give space for the diaphragm (D) to 
vibrate when the voice falls on it through the mouth- 
piece (C). 

From carbon one -eighth of an inch in thickness two 
round buttons are cut measuring three-quarters of an inch 
across. A small hole is bored in the centre of each button, 
and one of them is provided with a very small brass screw 
and nut, as shown at F F. One side of the button-hole is 

170 



TELEPHONES 



countersunk, so that the head of the screw will fit down 
into it and be flush with the face of the carbon. With a 
small three-cornered or square file cut the surface of the 
buttons with criss-cross lines, as shown at F F. When the 
buttons are mounted in the receiver these surfaces will face 
each other. Cut a small washer from felt or flannel, and 
place it in the bottomi of the hole in block A. Line the side 
of the hole with a narrow strip of the same goods; then 
place the button (F F) in the hole, pass the screw through the 
hole and through the block (A) , and make it fast with the 
nut, as shown at F. Place a thin, flat w^asher under the nut, 
and twist a fine piece of insulated copper wire between 
washer and nut for terminal connections, taking care that 
the end of the wire under the nut is bare and bright, so that 
perfect contact is assured. Since the practice of telephony 
involves such delicate and sensitive vibratory and electrical 
phenomena, it is best to solder all joints and unions wherever 
practicable, and so avoid the possibility of loose connections 
or corrosion of united wires. 

From very thin ferrotype plate cut a piece two inches 
square, and at the middle of it attach the other carbon but- 
ton by means of a small rivet which you can make from a 
piece of copper wire. Or a very small brass machine screw 
may be passed through the button and plate; then gently 
tapped at the face of the plate to rivet it fast, as shown 
at E. Lay the block down flat and partly fill the cavity 
with carbon granules until the button is covered. Do not 
fill up to the top of the hole. Over this lay the disk (D), so 
that the carbon button at the under side of it will fit in the 
top part of the hole between the sides of felt or fiannel. 



ELECTRICITY BOOK FOR BOYS 

Make the disk fast to the block (A) with small pins made by 
clipping ordinary pins in half and filing the ends. 

A slim bolt (G) is passed through the block (A) , and a wire 
terminal is caught under a nut and between a washer at 
the back of the block, as described for F. The japan or 
lacquer must be scraped away from the disk (D) where the 
bolt-head touches it, so that perfect electrical contact will 
be the result. 

A small tin funnel is cut and made fast to the face-plate 
(B), or if an electrical stipply-house is at hand a mouth-piece 
of hard rubber or composition may be had for a few cents. 
The block (B) is then screwed fast to A, forming the trans- 
mitter shown at Fig. 9. A¥hen this transmitter stands in a 
vertical position the granules, or small particles of carbon, 
drop down between the buttons of carbon, packing closely 
at the bottom of the cavity. At the middle they are loosely 
placed, and at the top there are none. As the high or low 
vibrations of the voice fall on the disk (D) they act accord- 
ingly on the carbon granules, which in turn conduct the 
vibrations to the rear carbon button, and, by the aid of 
electricity reproduce the same sound, in high or low tone, 
through the receiver at the other end of a line. 

This improved transmitter makes it possible to talk in a 
moderate tone of voice over distances up to one thousand 
miles, while with the old form of the instrument it was 
necessary to talk very loud in order to be heard only a few 
miles away. Where a portable apparatus is desired, this 
block may be attached to a box or an upright staff. 

This transmitter will not work when on its back or so 
that the funnel is on top, because the particles of carbon 

172 



TELEPHONES 



would settle on the rear button and not touch the front 
one. It is essential that the carbon grains should touch 
both buttons at the same time, and at the lower part of the 
cavity they should lie quite solid. It is not necessary, how- 
ever, to pack it in, for the vibratory action of the voice, or 
other sounds, will cause the particles to adjust themselves 
and settle in a compact mass. 

Another Form of Transmitter 

In Fig. II another style of transmitter is shown. It is 
assembled on the front of a box. This front or cover swings 
on hinges, and can be opened so that the mechanism in the 
interior of the box may be gotten at easily. 

A sectional view of this transmitter is shown in Fig. 12. 
A hole one inch and a half in diameter is cut in the cover (A). 
A round or square block (B) two inches and a quarter across 
and half an inch thick is made fast to the rear of the cover, 
and in this a hole is bored seven-eighths of an inch in diam- 
eter and one-quarter of an inch deep. 

The sides and bottom of this hole are lined with flannel 
or felt, and a carbon button with roughened surface, as 
shown at F F, is made fast in it by a small machine screw 
and nut (F). A diaphragm (D) is cut from thin ferrotype 
plate, and a carbon button is made fast to the middle of it 
by a small machine screw or a rivet made from soft copper 
or brass. When the block (B) has been screwed fast to A, 
place some granules of carbon in the space (H) ; then lay the 
diaphragm over the opening, and make it fast with small 
screws or pins driven around the edge. 

173 



ELECTRICITY BOOK FOR BOYS 

From a small tin funnel and a tin-can cap make a mouth- 
piece (C) by cutting a hole in the cap and slipping the funnel 
through it, then cutting the end of the funnel that projects 
through the hole and bending back the ears so that they 
lap on the inner side of the cap. These small ears may be 
soldered to the cap so as to hold the mouth-piece securely in 
place. From felt or flannel cut a washer the size of the 
can top and about three-eighths of an inch in width. Lay 
this over the diaphragm; then place the mouth-piece on it 
and fasten it to the door (A) with small screws. The use of 
this washer is to prevent any false vibrations in the mouth- 
piece affecting the sensitive diaphragm. Make a small hole 
through A and B and pass a bolt (E) through this hole, 
taking care to lap a thin piece of sheet -brass on the 
diaphragm (D), bending it over so that it will lie under the 
head of the bolt (E) . The diaphragm must be scraped where 
the metal touches it, so as to make perfect electrical con- 
nection between D and E. At the rear end of E arrange 
a washer and nut (G), so that the current passing in at G 
travels through E and D, then through the carbon buttons 
and granules, and out at F. 

From pine or white-wood one-quarter or three-eighths 
of an inch thick make a box four inches wide, six inches 
high, and two inches and a half deep. To the front of this 
attach a cover, which should measure a quarter of an inch 
larger all around than the width and height of the box. 
Use brass hinges for this work so that the cover may be 
opened. Fasten a transmitter to the front of the cover, or 
make one on the cover, as shown in Fig. 1 1 , and attach the 
box to a back-board or wall-plate five inches wide and 

. 174 



TELEPHONES 



.seven inches high made of pine or white- wood half an inch 
in thickness (see Fig. 13). 

At the left side of the box cut a slot through the wood, 
so that a lever and hook may project and work up and 
down. The end of this lever is provided with a hook on 
which a receiver may be hung, as shown in Fig. 13, and the 




175 



ELECTRICITY BOOK FOR BOYS 

inside mechanism is arranged as shown at Fig. 14. A is 
an angle-piece of brass or copper, which acts as a bracket 
and which is screwed fast to the inside of the box. B is the 
lever and hook, which is cut from a strip of brass. The 
attached end is made wider, and an ear (C), to which a wire 
is soldered, projects down beyond the screw. 

A view looking down on this lever and bracket is shown 
at Fig. 15. A is the bracket, B the lever, and E the screw 
or bolt holding the two parts together, with a thin copper 
washer between them to prevent friction. When the lever 
and bracket are made fast to the box, a spring (D) should 
be arranged, so that when the receiver is removed from the 
hook the lever will be drawn up to the top of the slot. A 
small contact-plate (F) is made of brass, and fastened at the 
lower end of the slot. On this the lever should rest w^hen 
the receiver is on the hook. A contact-wire is soldered to 
this plate, which in turn is screwed fast to the inside of 
the box. This mechanism is part of a make-and-break 
switch to cut out and cut in the bells or telephone, and 
will be more clearly understood by referring to the diagram 
in Fig. 17. At the right side of the box a small push-button 
is made fast, and this, with two binding-posts at the top 
and four at the underside of the box, will complete the 
exterior equipment of one end of a line. 

The construction of the push-button is shown in Fig. 16, A 
being the box and B the button which passes through a small 
hole made in the side of the box. C is a strip of spring- 
brass screwed fast to the box. It must be strong enough 
to press the small bone or hard rubber button towards the 
outside of the box. A wire is caught under one screw-head, 

176 



TELEPHONES 



and another one is passed under the screw-head which holds 
the other spring (D) to the box. When the button (B) is 
pushed in, it brings spring C into contact with D, and the 
circuit is closed. Directly the finger is removed from B 
the spring (C) pushes it out and breaks the circuit. This 
button is used only in connection with the call-bells, and has 
nothing to do with the telephone. The wires leading from 
the interior of the box pass through the wall-plate and along 
in grooves to the foot of the binding-posts, which are ar- 
ranged below the box on the back-board, as shown in Fig. 13. 
A buzzer or bell is made fast to the inside of the box, 
unless it is too large to fit conveniently, in which case it 
may be attached to the wall above or below the box. 

The Wiring System 

Fig. 17 shows the wiring system for this outfit, which, 
when properly set up and connected, should operate on a 
circuit or line several miles in length, provided that the 
batteries are strong enough. 

This system may be installed in the box shown in Fig. 13, 
the flexible cord containing two wires being attached to the 
binding-posts at the top of the box and to the posts at the 
end of the receiver. This system differs from the one shown 
in Fig. 6 only in the addition of receivers T and T 2, and in 
the substitution of the automatic lever-switches (L S and 
L S 2) for the plain switches (S and S 2) in Fig. 6. When the 
line is "quiet" the receiver (R) should be hanging on the 
lever- switch (L S) , which rests on the contact-plate (A) . At 
the opposite side of the line the receiver (R 2) hangs on the 

177 







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(A 




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(A 




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CO H 
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w 

O 



TELEPHONES 



lever-switch (L S 2), which in turn rests on the contact- 
plate (A A). This puts the bell circuit in service. 

If the boy at the left wishes to calLup the boy at the 
right he removes the receiver (R) from the hook (L S) and 
presses on the button (P B). This closes the circuit through 
the battery (C C C) , and operates the electric buzzer or bell 
(E B 2) at the other end of the system, through line No. i 
and line No. 2. The operation may be clearly understood 
by following the lines in the drawing with a pointer. The 
boy at the left may keep on calling the boy at the right so 
long as the receiver (R 2) hangs on the lever (L S 2) and holds 
it down against the plate (A A) . But directly the receiver 
(R 2) is removed, the lever (L S 2) flies up — being drawn up- 
ward by the spring (D) shown in Fig. 14 — and closes the tele- 
phone circuit through the spring-contact (B B), at the same 
time cutting out the bell circuit. The boy at the left having 
already removed his receiver, the telephone circuit is then 
complete through lines Nos. i and 2 and batteries C C C and 
C 2 C 2 C 2 , the boys at both ends speaking into the trans- 
mitters and hearing through the receivers. The contacts 
B and B B are made from spring-brass or copper, and are 
attached inside the boxes at the back, so that when the 
levers are up contact is made, but when down the circuit 
is broken or opened. In Fig. 18 an interior view of a box 
is shown, the door being thrown open and. the receiver left 
hanging on the hook. 

The arrangement of the several parts will be found con- 
venient and easy of access. E B is the electric buzzer, L S 
the lever-switch, P B the push-button, T the transmitter, 
and R the receiver. Nos. i, 2, 3, 4, 5, 6, 7, 8 are binding- 

179 




TELEPHONE INSTALLATION. INTERIOR VIEW OF BOX 

i8o 



TELEPHONES 



posts or terminals, and B is the spring - contact against 
which the lever-switch (L S) strikes when drawn up by the 
spring (D). 

The wires that pass from 6 to 7 and from 4 to 8 should be 
soldered fast to one side of the hinge, and those running 
from the terminals or nuts at the back of the transmitter (T) 
to 7 and 8 should be similarly secured. Small brass hinges 
are not liable to become corroded at the joints, but to insure 
against any such possibility the ends of several fine wires 
may be soldered to each leaf of the hinge, so that when the 
door is closed the wires will be compressed between the 
hinge-plates. For long-distance commimication it will be 
necessary to install an induction-coil, so that the direct cur- 
rent furnished by the batteries, in series with the trans- 
mitter, can by induction be transformed into alternating 
current over the lines connecting the two sets of apparatus. 
This system is somewhat more complicated and requires 
more care in making the connections, but once in operation 
it will be found far superior to either of the systems hitherto 
described. 

A Telephone Induction-coil 

It will be necessary to make two induction-coils, as de- 
scribed in chapter iv., page 62, Fig. 8. A telephone coil 
for moderately long-distance circuits is made on a wooden 
spool turned from a piece of wood three inches and a half 
long and one inch square, as shown at Fig. 19. The core- 
sheath is turned down so that it is about one-sixteenth of 
an inch thick. This spool is given a coat or two of shellac, 

181 



ELECTRICITY BOOK FOR BOYS 



and two holes are made at each end, as shown in the draw- 
ing. The first winding or primary coil is made up of two 
layers of No. 20 double-insulated copper wire, one end pro- 
jecting from a hole at one end of the spool, the other from 
a hole at the other end. This coil is given two or three 
thin coats of shellac to bind the strands of wire and thor- 
oughly insulate them, and over the layer a piece of paper 
is to be wrapped and shallacked. The secondary coil is 
made up of twelve layers of No. 34 silk-insulated copper 
wire, and between each layer a sheet of paper should be 
wound so that it will make two complete wraps. Each 
paper separator should be given a coat of shellac or hot 
paraffine; then the turns of wire should be continued just 
as thread is wound upon a spool, smoothly, closely, and 
evenly, until the last wrap is on. Three or four wraps of 
paper should be fastened on the coil to protect it, and it 
may then be screwed fast inside a box. The core -hole 
within the coil should be packed with lengths of No. 24 soft 
Swedes iron wire three inches and a half long. In Fig. 19 
the wires are shown projecting from the end of a spool, and 
Fig. 20 depicts a completed telephone induction-coil. The 
installation of the induction-coils is shown in Fig. 21. 

The wiring is comparatively simple, and may be easily 
followed if the description and plan are constantly consulted 
when setting up the line. R and R2 are the receivers, T 
and T 2 the transmitters, C i and C 2 the batteries, E B and 
E B 2 the buzzers or bells, P B and P B 2 the push-buttons, 
and L S and L S 2 the lever-switches. For convenience of 
illustration the induction-coils are separated. The primary 
coil (PC) is indicated by the heavy spring line and the sec- 

182 



ELECTRICITY BOOK FOR BOYS 

ondary coil (S C) by the fine spring line. When the line is 
"dead" both receivers are hanging from the hooks of the 
lever-switches. If the boy at the left wishes to call the boy 
at the right he lifts the receiver (R) from the hook (L S) and 
presses the button (P B) . This throws the battery (C i C i C i ) 
in circuit with lines Nos. i and 2, and operates the buzzer 
(E B 2) . When the boy at the right lifts his receiver (R 2) from 
the hook (LS2), the bell circuit is cut out and the 'phone 
circuit is cut in. When the lever-switches are drawn up 
against the contact-springs (A, B, and C) and A A, B B, and 
C C) , both batteries are thrown into circuit with the trans- 
mitters at their respective ends through the primary coils 
(P C and P C 2). By inductance through the secondary coils 
(SC and SC 2), lines Nos. i and 2 are electrified, and when 
the voice strikes the disks in the transmitters the same tone 
and vibration is heard through the receivers at the other 
end of the line. While conversation is going on the batteries 
at either end are being drawn upon or depleted ; but as soon 
as the receivers are hung on the hooks and the lever-switches 
are drawn away from the contact-springs, the flow of current 
is stopped. The buzzers or bells consume but a small 
amount of current when operated, and in dry cells the active 
parts recuperate quickly and depolarize. The greatest 
drain on a battery, therefore, is when the line is closed for 
conversation. 

An Installation Plan 

A simple manner in which to install this apparatus in 
boxes is shown in Fig. 22. The box is depicted with the 
front opened and with the receiver hanging on the hook. 

184 



TELEPHONES 



When the lever-switch (L S) is down it rests on the contact- 
spring (A) , thus throwing in the bell circuit. When the boy 
at the other end of the line pushes the button on his box 




TO BATTtRY 

fig. 22 

it operates the buzzer (E B) . This can be understood by fol- 
lowing with a pointer the wires from the buzzer to the 
outlet-posts (Nos. i and 3) at the bottom of the wall-plate. 
When the receiver (R) is lifted from the hook (L S) , it cuts 

^85 



ELECTRICITY BOOK FOR BOYS 

out the bell circuit and cuts in the telephone circuit, through 
the spring-contacts (B and C). This circuit may easily be 
followed through the wires connecting transmitter, receiver, 
induction-coil, and batteries. The heavy lines leading out 
from the induction-coil are the primary coil wires, and the 
fine hair lines are those forming the secondary coil. The 
medium lines are those that connect the binding - posts, 
batteries, and lines. 

When the bell circuit is connected the impulse coming 
from the other end of the line enters through wire No. lo 
to post No. 3, thence to strip E and plate G, and so on to 
EB, which it operates. The current then passes from EB 
to contact A, through L S to post No. i , and out on wire 
No. II. 

To operate the buzzer at other end of the line the button 
(P B) is pushed in. This moves the spring (E) away from the 
plate (G), and brings it into contact with F. This connects 
the circuit through the battery wire (No. 8) to post No. i to 
line No. ii without going into the box, and from wire No. 
9 to post No. 2 ; thence to hinge No. 7 to plate F, through 
E, down to post No. 3, and out through wire No. 10. In 
this manner the current is taken from the batteries at the 
foot of wires Nos. 8 and 9, and used to ring the buzzer at the 
other end of the line. 

When the hook (L S) is up the circuit is closed through T, 
I C, and battery. The current runs from the battery through 
wire No. 8 to post No. i , to L S, through C and primary coil 
out to hinge No. 6, through transmitter to hinge No. 7, to 
post No. 2, and back to battery through wire No. 9. 

By inductance the sound is carried over the line, in at 



TELEPHONES 



wire No. lo, to post No. 3, through secondary coil to post 
No. 4, through receiver R to post No. 5, through B and 
LS to post No. I, and out through wire No. 11. At the 
other end of the line it goes through the same parts 
of the apparatus. 

A Portable Apparatus 

For convenience it is often desirable to have a portable 
transmitter, and so avoid the inconvenience of having to 
stand while speaking. A neat portable apparatus that will 
stand on a ledge or table, and which may be moved about 
within the radius of the connecting lines, is shown in Fig. 23. 

The wooden base is four inches square and the upright 
one inch and a half square. The stand is twelve inches 
high over all, and on the bottom a plate of iron or lead must 
be screwed fast to make it bottom-heavy, so that it will not 
topple over. 

The lever-switch may be arranged at the back of the 
upright and the push-button at the front near the base, as 
shown at A. The wall-box contains the buzzer and induc- 
tion-coil, and within it the wiring is arranged from the port- 
able stand to the batteries and line as shown at C. This 
illustration is too small, however, to show the complete 
wiring, and the young electrician is therefore referred to 
Fig. 22. The battery (B) is composed of as many dry or 
wet cells as may be required to operate the line. These 
must be connected in series at both ends. At D a rear view 
of the upright and transmitter is shown to illustrate the 
manner in which the wiring can be done. If a hollow up- 

187 




A PORTABLE APPARATUS 

i88 



TELEPHONES 



right is made of four thin pieces of wood a much neater 
appearance may be secured by enclosing the wires. 

In all of these telephone systems one wire must lead to 
the ground, or be connected with a water-pipe, taking care, 
however, to solder the wire to a galvanized pipe so that 
perfect contact will be the result. If the wire is carried 
directly to the ground it must be attached to a plate, which 
in turn is buried deep enough to reach moist earth, as 
described in the chapter on Line and Wireless Telegraphs, 
page 215. 

Care and accuracy will lead to success in telephony, but 
one slip or error will throw the best system out of order 
and render it useless. This, indeed, applies to all electrical 
apparatus; there can be no half-way; it will either work 
or it won't. 



Chapter IX 

LINE AND WIRELESS TELEGRAPHS 

A Ground Telegraph 

NEARLY every boy is interested in telegraphy, and it 
is a fascinating field for study and experimental work, 
to say nothing of the amusement to be gotten out of it. 
The instruments are not difficult to make, and two boys 
can easily have a line between their houses. 

The key is a modified form of the push-button, and is 
simply a contact maker and breaker for opening and clos- 
ing an electrical circuit. A practical telegraph - key is 
shown in Fig. i, and in Fig. 2 is given the side elevation. 

The base-board is four inches wide, six inches long, and 
half an inch in thickness. At the front end a small metal 
connector-plate is screwed fast, and through a hole in the 
middle of it a brass-headed upholsterer's tack is driven for 
the underside of the key to strike against. Two L pieces 
of metal are bent and attached to the middle of the board 
to support the key-bar, and at the rear of the board an- 
other upholsterer's tack is driven in the wood for the end 
of the bar to strike on and make a click. The bar is of 
brass or iron, measuring three-eighths by half an inch, and 
is provided with a hole bored at an equal distance from each 

190 



LINE AND WIRELESS TELEGRAPHS 

end for a small bolt to pass through, in order to pivot it 
between the L plates. A hole made at the forward end 
will admit a brass screw that in turn w411 hold a spool-end 




to act as a finger-piece. The screw should be cut off and 
riveted at the underside. A short, strong spring is to be 
attached to the back of the base-block and to the end of 
the key-bar by means of a hook, which may be made from 



ELECTRICITY BOOK FOR BOYS 

a steel- wire nail flattened. It is bound to the top of the 
bar with wire, as shown in Figs. 2 and 3. 

The incoming and outgoing wires are n?ade fast to one 
end of the connector-plate and to one of the L pieces that 
support the key. When the key is at rest the circuit is 
open, but when pressed down against the brass tack it is 
closed, and whether pressed down or released it clicks at 
both movements. A simple switch may be connected wdth 
the L-plate and the connection-post at the opposite side of 
the key-base, so that, if necessary, the circuit may be 
closed. Or an arm may be caught under the screw at the 
L-plate, and brought forward so that it can be thrown in 
against a screw-head on the connector-plate, as shown in 
Fig. 3. The screw-head may be flattened with a file, and 
the underside of the switch bevelled at the edges, so that 
it will mount easily on the screw. 

In Fig. 4 (page 191) a simple telegraph-sounder is shown. 
A base-board, four inches wide, six inches long, and seven- 
eighths of an inch in thickness, is made of hard- wood, and 
two holes are bored, with the centres two inches from one end, 
so that the lower nuts of the horseshoe magnet will fit in 
them, as shown in Fig. 5. This allows the yoke to rest flat 
on the top of the base, and with a stout screw passed down 
through a hole in the middle of the yoke and into the wood 
the magnets are held in an upright position. 

From the base-block to the top of the bolt the magnets 
are two inches and a quarter high. The bar of brass or 
iron to which the armature (A in Fig. 5) is attached is four 
inches and a half in length and three-eighths by half an 
inch thick. At the middle of the bar and through the 



LINE AND WIRELESS TELEGRAPHS 

side a hole is bored, through which a small bolt may be 
passed to hold it between the upright blocks of wood. At 
the front end two small holes are to be bored, so that its 
armature may be riveted to it with brass escutcheon-pins 
or slim round-headed screws. The heads are at the top 
and the riveting is underneath. A small block of wood is 
cut, as shown in Fig. 6, against which the two upright 
pieces of wood are made fast. This block is two inches 
and a half long, one inch and a quarter high, and seven- 
eighths of an inch wide. The laps cut from each side are 
an inch wide and a quarter of an inch deep, to receive the 
uprights of the same dimensions. 

At the top of this block a brass-headed nail is driven 
for the underside of the bar to strike on. A hook and spring 
are to be attached to the rear of the sounder-bar, as de- 
scribed for the key, and at the front of the base two binding- 
posts are arranged, to which the loose ends of the coil-wdres 
are attached. 

Just behind the yoke, and directly under the armature- 
bar, a long screw is driven into the base-block, as shown 
at B in Fig. 5. It must not touch the yoke, and the head 
should be less than one-eighth of an inch below the bar 
when at rest. On this the armature-bar strikes and clicks 
when drawn to the magnets. The armature must not 
touch the magnets; otherwise the residual magnetism 
would hold it down. The screw must be nicely adjusted, 
so that a loud, clear click will result. 

When the sounder is at rest the rear end lies on the brass 
tack in the block, and the armature is about a quarter of 
an inch above the top of the magnets. The armature is of 
13 193 




T|Cr.3 



TiGr.2 




TiGr.5 




TELEGRAPH KEY AND SOUNDER 
194 



LINE AND WIRELESS TELEGRAPHS 

soft iron, two inches and a half long, seven-eighths of an 
inch wide, and an eighth of an inch thick. These small 
scraps of metal may be procured at a blacksmith's shop, 
and, for a few cents, he will bore the holes in the required 
places; or if you have a breast or hand drill the metal 
may be held in a vise and properly perforated. 

By connecting one wire from the key directly with one of 
the binding-posts of the sounder, and the other with the 
poles of a battery, and so on to the sounder, the apparatus 
is ready for use. By pressing on the key the circuit is 
closed, and the magnetism of the sounder-cores draws the 
armature down with a click. On releasing the key the bar 
flies back to rest, having been pulled down by the spring, 
and it clicks on the brass tack-head. These two instru- 
ments may be placed any distance apart, miles if necessary, 
so long as sufficient current is employed to work the sounder. 
Two sets of instruments must be made if boys in separate 
houses are to have a line. Each one must have a key, 
sounder, and cell, or several cells connected in series to form 
a battery, according to the current required. 

In the plan of the telegraph-line connections (Fig. 7, page, 
196) a clear idea is given for the wiring; and if the line and 
return wires are to be very long, it would be best to have them 
of No. 14 galvanized telegraph-wire, copper being too ex- 
pensive, although much better. These wires must not touch 
each other, and when attached to a house, barn, or trees, 
porcelain or glass insulators should be used. If nothing 
better can be had, the necks of some stout glass bottles may 
be held with wooden pins or large nails, and the wire twisted 
to them, as shown in Fig. 8. When the line is not in use 

195 



ELECTRICITY BOOK FOR BOYS 

the switches on both keys should be closed; otherwise it 
would be impossible for the boy having the closed switch 
to call up the boy with the open one. Take great care in 
wiring your apparatus to study the plan, for a mi^connected 
wire will throw the whole system out of order. 



Ti^7- 




CELL 

HOUSE N2I 



CE.LL 

lOUSE N92 



To Operate the line see that all switches are closed and 
that the connections are in good condition. When the boy 
in house No. 2 wants to call up his friend in house No. i 
he throws open the switchon key, as shown in the plan, 
and by pressing down on the finger-key his sounder and 
that in house No. i click simultaneously. As soon as he 
raises or releases the key the armatures rise, making the 
up-click. If he presses his key and releases it quickly the 
two clicks on the sounder in house No. i are close together; 
this makes what is called a dot. If the key is held down 

196 



LINE AND WIRELESS TELEGRAPHS 

longer it makes a long time between clicks, and this is called 
a dash. The dot and dash are the two elements of the 
telegraphic code. You will understand that the boy in 
house No. 2 hears just what the one in No. i is hearing, 
since the electric current passing through both coils causes 
the magnets to act in unison. So soon as the operator in 
house No. 2 has finished he closes his switch, and the other 
in house No. i opens his switch on the key and begins his 
reply. This is the simple principle of the telegraph, and 
all the improved apparatus is based on it, no matter how 
complicated. The complete Morse alphabet is appended : 

The Morse Telegraph Code 

AB CDEFG H 

• — -— • • • • • • — • • • • — • — — • • • • • 

I J KLM NO P 

Q R S T U V W 

• • — • • --.• • • • • ——' • • — " • • • — • — — 

X Y Z & I 

• — •■ •••• •••• •••• • — — -^— — ^ • 



Any persevering boy can soon learn the dot-and-dash 
letters of the Morse code, and very quickly become a fairly 

197 



ELECTRICITY BOOK FOR BOYS 

good operator. Telegraphic messages are sent and re- 
ceived in this way, and are read by the sound of the cHcks. 
Various kinds of recording instruments are also employed, 
so that when an operator is away from his table the auto- 
matic recorder takes down the message on a paper tape. 
In the stock-ticker, employed in brokerage offices, the 
recording is done by letters and numerals, and the paper 
tape drops into a basket beside the machine, so that any 
one picking up the strip of paper can see the quotations 
from the opening of business up to the time of reading 
them. These quotations are sent out directly from the 
floor of the exchanges, and by the action of one man's hand 
thousands of machines are set in operation all over the city. 

Perhaps the most unique and wonderful telegraphic 
signal - apparatus is that located on the floor of the New 
York Produce Exchange and the Chicago Exchange. The 
dials, side by side, are operated by direct wire from Chicago. 
When the New York operator flashes a quotation it appears 
simultaneously on the New York dial and simultaneously 
on the Chicago dial, and vice versa. 

Electrical instruments are not the only means by which 
the Morse alphabet may be transmitted, for in some in- 
stances instruments would be in the way, while in others 
the wires might be down and communication cut off. 

This is interestingly illustrated by an event in Thomas 
A. Edison's life. When he was a boy and an apprentice 
telegraph operator on the Grand Trunk Line, an ice- jam 
had broken the cable between Port Huron, in Michigan, 
and Sarnia, in Canada, so that communication by elec- 
tricity was cut off. The river at that point is a mile and 

198 



LINE AND WIRELESS TELEGRAPHS 

a half wide, the ice made the passage impossible, and there 
was no way of repairing the cable. Edison impulsively 
jumped on a locomotive standing near the river-bank and 
seized the whistle-cord. 

He had an idea that blasts of the whistle might be broken 
into long and short sounds corresponding to the dots and 
dashes of the Morse code. In a moment the whistle sounded 
over the river: "Toot, toot, toot, toot, — ^toot, tooooot, — 
tooooot — ^tooooot — ^toot, toot — toot, toot." " Halloo, Sarnia ! 
Do you get me? Do you hear what I say?" 

No answer. 

"Do you hear what I say, Sarnia?" 

A third, fourth, and fifth time the message went across, 
to receive no response. Then suddenly the operator at 
Sarnia heard familiar sounds, and, opening the station door, 
he clearly caught the toot, toot of the far-away whistle. 
He found a locomotive, and, mounting to the cab, responded 
to Edison, and soon messages were tooted back and forth 
as freely as though the parted cable were again in operation. 

Some years ago the police of New York were mystified 
over a murder case. The man they suspected had not fled, 
but was still in his usual place, and attending to his busi- 
ness quite as though nothing had happened to connect him 
with the tragedy. 

Detectives in plain clothes had been following him and 
watching closely his every move in and out of restaurants 
and shops and at social affairs; but not the slightest proof 
could be secured against him. 

One noon-time they followed him into a cafe, where he 
had gone with a friend. The detectives took seats near 

199 



ELECTRICITY BOOK FOR BOYS 

him, but each of them sat at different tables in the room 
full of people. 

When in the cafe the suspect sat next the wall, a habit 
the detectives had noticed. Consequently, only those per- 
sons who sat at one side of him or directly in front could 
see his. face. During the time they were in the restaurant 
the detectives communicated with each other by tapping 
on the table tops with a lead-pencil; and something the 
man said, which the nearest detective heard, led to the 
climax. One detective rose, paid his check, and loitered 
near the door; another got up a little later and sauntered 
out, but returned with a cardboard sign. Going over to 
the table where the suspected criminal and his friend sat, 
he deliberately tacked it on the wall above them, then 
went out again, leaving the third detective to watch the 
face of the man as he read: 

$1000 REWARD 

for information leading to the arrest of the murderer of 

on March , 1876 

The man cast a glance about the restaurant, then said 
to his companion: "Did I show any signs of agitation?" 
The third detective rose, stepped over to the man, tapped 
him on the shoulder, and said, " I want you." There would 
have been a scene of violence had not the other two de- 
tectives closed in on the man, and within six months he 
paid the penalty of his crime. 

If it had not been for the dot-and-dash alphabet, tapped 
out with lead-pencils, the detectives could not have com- 
municated; but like Edison, they used the means at hand 
to open up and carry on a silent conversation. 

200 



LINE AND WIRELESS TELEGRAPHS 

Wireless Telegraphy 

Everybody nowadays understands that wireless telegra- 
phy means the transmission of electrical vibrations through 
the ether and earth without the aid of wires or any visible 
means of conductivity. The feat of senciling an electrical 
communication over thousands of miles of wire, or through 
submarine cables, is wonderful enough, for all that custom 
has made it an every-day miracle. To accomplish this same 
end by sending our messages through the apparently empty 
air is indeed awe-inspiring and almost beyond belief. And 
yet we know that wireless telegraphy is to-day a real scien- 
tific fact. 

At first sight it would seem, that the instruments must 
be complicated and necessarily beyond the ability of the 
average boy to make, and far too expensive as well. As a 
matter of fact, the young electrician may construct his wire- 
less apparatus at a very moderate cost, it being understood 
that the sending and receiving poles may be mounted on a 
housetop or barn. 

But first let us consider the theory upon which we are 
to work. There is no doubt but that electricity is the high- 
est known form of vibration — so high, indeed, that as yet 
man has been unable to invent any instrument to record 
the number of ptilsations per second. This vibration will 
occur in, and can be sent through, the ordinary form of con- 
ductor, such as metals, water, fluids and liquids, wet earth, 
air and ice. Also through what we call the ether. 

Now the ether of the atmosphere, estimated to be fifteen 
trillion times lighter than air, is the medium through which 

201 



ELECTRICITY BOOK FOR BOYS 

the electrical vibrations pass in travelling in their radial 
direction from a central point, corresponding to the ripples 
or wavelets formed when a pond or surface of still wa- 
ter is disturbed. Ether is so fine a substance that the or- 
gans of sense are not delicate enough to detect it, and 
it is of such a volatile and uneasy nature that it is 
continually in motion. It vibrates under certain condi- 
tions, and when disturbed (as by a dynamo ) it undoubt- 
edly forms the active principle of electricity and mag- 
netism. 

James Clark Maxwell believed that magnetism_, electricity, 
and light are all transmitted by vibrations in one common 
ether, and he finally demonstrated his theory by proving 
that pulsations of light, electricity, and magnetism differed 
only in their wave lengths. In 18,87 Professor Hertz suc- 
ceeded in establishing proof positive that Maxwell's theories 
were correct, and, after elaborate experiments, he proved 
that all these forces used ether as a common medium. 
Therefore, if it were not for the ether, wireless telegraphy, 
with all its wonders, would not be possible. We understand, 
then, that the waves of ether are set in motion from a cen- 
tral disturbing point, and this can be accomplished only 
by means of electrical impulse. 

Suppose that we strike a bell held high in the air. The 
sound is the result of the vibrations of its mass sending its 
pulsating energy through the air. The length of the sound- 
waves is measured in the direction in which the waves are 
travelling, and if the air is quiet and not disturbed by 
wind the sound will travel equally in all directions. The 
sound of a bell will not travel so well against a wind as it 

202 



LINE AND WIRELESS TELEGRAPHS 



will with it, just as thp ripples on a pond would be checked 
by an adverse set of wavelets. 

Now the ether can be made to vibrate in a similar man- 
ner to the air by a charge of electricity oscillating or surg- 
ing to and fro on a wire several hundred thousand times in 
a second. These oscillations strike out and affect the sur- 
rounding ether, so that, according to the intensity of the 
disruptive charge at the starting-point, the ether waves 
ma}^ be made to reach near or distant points. 

This is, perhaps, more clearly shown by the action of a 
pendtilum. In Fig. 9 the rod and ball are at rest, but if 
drawn to one side and released it swings over to the other 
side nearly as far away from its central position of rest as 
from the starting-point. If allowed to swing to and fro it 
will oscillate until at last it will come to rest in a vertical 
position. This same oscillation (oscillation being a form of 
vibration) takes place in the water when a stone has been 
flung into it, and in the ether when affected by the electrical 
discharge. In Fig. 10 are shown the principal varieties of 
vibration — the oscillating, pulsating, and alternating. 

It is known that if these oscillations are damped, so that 
the over -intense agitation of the central disturbance is 
lessened, a new series of vibrations, such as the pulsating or 
alternating, is set up, and these secondary vibrations pos- 
sess the power to travel around the world — yes, and perhaps 
to other worlds in the planetary cosmos. 

The study of ether disturbances, wave currents, oscillat- 
ing currents, and the other phenomena dependant upon 
this invisible force is most interesting and fascinating, and 
were it possible to devote more space to this topic several 

203 




rier.9 




Ti^io 



PUL5ATING- 




ALTtRNATINQ- 



NY 



T\Q:\l 



OSCILLATION AND VIBRATION 
204 



LINE AND WIRELESS TELEGRAPHS 

chapters coiild be written on the scientific theory of wire- 
less telegraphy.* 

The principle difference between wire, or line, and wire- 
less telegraphy is that the overhead wire, or underground or 
submarine cable, is omitted. In its stead the ether of the 
air is set in vibratory motion by properly constructed in- 
struments, and the communication is recorded at a distance 
by instruments especially designed to receive the trans- 
mitted waves. 

It seems to be the popular impression that a wireless mes- 
sage sent from one point to another travels in a straight 
line, as indicated by Fig. ii, B representing Boston, which 
receives the message from N. Y., or New York. As a matter 
of fact, if several sets of wireless receiving instruments 
were located on the circumference of a circle the same dis- 
tance from New York in all directions, or even at nearer 
or farther points, they would all receive the same message. 
Instead of travelling in one direction, the ether waves are 
set in motion by the electrical disturbance, just as water is 
agitated by the stone thrown into it. The ripples, or wave- 
lets, are started from the central point of disturbance and 
radiate out, so that instead of reaching Boston only the 
waves travel over every inch of ground, or air space, in all 
directions, and would be recorded in every town and vil- 
lage within the sphere of energy set up by the original force 
that put the ether waves in motion. The stronger this 
initial force the wider its field of action. This is shown at 

* For further information on this subject the student is referred to such 
well-known books as Signalling Across Space Without Wires, by Prof, 
Oliver J. Lodge, and Wireless Telegraphy, by C. H. Sewall. 

205 



ELECTRICITY BOOK FOR BOYS 

Fig. 12, which is an area comprising Philadelphia, Pitts- 
burg, Buffalo, Washington, and other cities. Moreover, the 
waves of electrical disturbance would carry far beyond in 
all directions, taking in the cities of the north, south, and 







-^"^^^-X^ 




west, and at the east, going far out to sea, beyond Boston 
harbor and below Cape Hatteras, where ships carrying re- 
ceiving instruments could pick up the messages. Like the 

206 



LINE AND WIRELESS TELEGRAPHS 

ripples on the water, the radiating waves, or rings, become 
larger as they reach out farther and farther from the centre 
of disturbance, until at last they are imperceptible, and 
lose their shape and force. 

At great distances, therefore, the ether disturbance be- 
comes so slight that it is impossible to record the vibration 
or message sent out; and until some improved forms of ap- 
paratus and coherer are invented, or the original disturbing 
force is enormously increased, it will be impossible to send 
messages at longer distances than four or five thousand 
.miles from a central point. Both Marconi and De Forrest 
assert that they are perfecting coherers which will make 
it possible to girdle the earth with a message, and that 
within the next few years an aerogram may be sent out from 
a station, and, after instantly encircling the earth and being 
recorded during its passage at all intermediate stations, it 
will return and be received at the original sending-point. 
This, of course, is a matter of future achievement; but now 
that messages across the Atlantic are a commercial fact, it 
seems quite possible that the greater feat of overriding space 
and reaching any point on the earth's surface will soon be 
a reality. And now to proceed from theory to the con- 
struction of a practical wireless apparatus having a radial 
area of action over some ten or fifteen miles. 

The principal parts of a wireless apparatus include the 
antennae (or receiving and sending poles with their terminal 
connections), the induction-coil, strong primary batteries 
or dynamo, the coherer and de- coherer, the telegraph 
key and sounder (or a telephone receiver), and the neces- 
sary connection wires, binding-posts, and ground -plates. 

207 



ELECTRICITY BOOK FOR BOYS 

A large induction-coil with many layers of fine insulated 
wire will be necessary for the perfect operative outfit. The 
most practical coil for the amateur is a Ruhmkorff induc- 
tion-coil. (See the directions and illustrations for con- 
structing this coil, beginning on page 59 of chapter iv.) 

The sending apparatus is practically the same in all out- 
fits, and consists of a source of electrical energy, such as 
a battery, or dynamo, the essential induction-coil and ad- 
justable spark-gap between the brass balls on terminal rods, 
and the make-and-break switch, or telegraph-key. 

It is in the various forms of coherers and receiving ap- 
paratus that the different inventors claim superiority and 
originality. The systems also differ in their theory of har- 
monic tuning or vibratory sympathy. This is accomplished 
by means of coils and condensers, so that the messages 
sent out on one set of instruments will not be picked up or 
recorded by the receiving apparatus of competitors. 

Having made or purchased an induction-coil of proper 
and adequate size, it will now be necessary to construct the 
parts so that an adjustable spark-gap may be secured. 

Make a hollow wooden base for the induction-coil to rest 
on. It should be a trifle longer than the length of the coil 
and about seven inches wide. This may be made from 
wood half an inch thick. The base should be two inches 
high, so that it will be easy and convenient to make wire 
connections under it. Mount the induction-coil on the 
base and inake it fast with screws, arranging it so that the 
binding-posts are on the side rather than at the top of the 
coil, as shown in Fig. 13. 

Cut a thin board and mount it across the top of the in- 

208 



LINE AND WIRELESS TELEGRAPHS 

duction-coil on tYvo short blocks, and to this attach two 
double-pole binding-posts (P P) . The fine wires from the 
induction-coil are made fast to the foot of each post, and 
from the posts the aerial wire (A W) and ground wire (G W ) 
lead out. 

Fasten two binding-posts at the forward corners of the 
base, and to them make connection- wires fast to the heavy 
or primary wires of the coil. Wires B and C lead out from 
these posts to the battery and key, and to complete this 
part of the sending, or transmitting apparatus it will be 
necessary to have two terminal rods and balls attached to 
the top of the binding-posts (P P) . This part of the appara- 
tus is generally called the oscillator, and the rods are bal- 
anced on the posts, so that they can be moved in order to 
increase or diminish the space (SG), or spark-gap, between 
the brass balls. 

When, after experiment, the proper space has been de- 
termined, the set screw at the top of the posts will hold 
the terminal rods securely in place. 

Obtain a piece of brass, copper, or German - silver rod 
three-sixteenths of an inch in diameter. Now cut two 
short rods, each six inches long, and two inches from one 
end flatten the rods with a hammer, as shown at A in Fig. 
14. Flatten the rod in two places at the other end, as shown 
at B B in Fig. 14; then bore holes through the flattened 
parts (A) , so that the binding-screws at the top of the posts 
(P P) will pass through them. 

Obtain two brass balls from one to one inch and a half 
in diameter. If they are solid or cast brass they may be 
attached to the ends of the terminal rods by threading, so 
14 209 



ELECTRICITY BOOK FOR BOYS 

that it will be easy to remove them. If the balls are of 
spun sheet-metal it will be necessary to solder them fast 
to the ends of the rods, and, when polishing the balls, the 
rods will have to be removed from the binding-posts. It 
is imperative that the balls should be kept polished and in 
bright condition at all times, to facilitate the action of the 
impulsive sparks. 




FiGr.(5 




FlGrl4 



2IO 



LINE AND WIRELESS TELEGRAPHS 

To counterbalance these balls there should be handles at 
the long ends of the rods. These handles may be of wood, 
or made of composition molded directly on the rods. A 
good composition that can be easily made and molded is 
composed of eight parts plaster of Paris and two parts of 
dextrin made into a thick paste with water. The dextrin 
may be purchased at a paint-store, and is the color of light- 
brown sugar. Mix the dry plaster and dextrin together, 
so that they are homogeneous; then add water to make 
the pasty mass. Use an old table-knife to apply the wet 
-composition to the bars. The flattened parts will help 
to hold the mass in place until it sets. It is best to make 
two mixtures of the paste and put one on first, leaving it 
rough on the surface, so that the last coat will stick to it. 
When the last coat is nearly dry it may be rubbed 
smooth with the fingers and a little water, or allowed to dry 
hard, and then smoothed down with an old fixle and sand- 
paper. 

If solid brass balls are used for the terminals the com- 
position handles may be made heavier; but in any event 
the proper amount of composition should be used, so that 
when the rod is balanced on a nail or piece of wire passed 
through the hole it will not tip down at one end or the 
other, but will remain in a horizontal position. ' 

The overhead part of the apparatus employed to collect 
the electric waves is called the antennae, and in the various 
commercial forms of wireless apparatus this feature differs. 
The general principle, however, is the same, and in Figs. 
15, 16, 17, and 18 some simple forms of construction are 
shown. 

211 



ELECTRICITY BOOK FOR BOYS 

Great care must be taken to properly insulate the rod, 
wire, or fingers of these antennse, so that the full force of 
the vibration is carried directly down to the coherer and 
sounder or receiver. For this purpose, porcelain, glass, or 
gutta-percha knobs must be employed. 

In Fig. 15 the apparatus consists of an upright stick, a 
cross-stick, and a brace, or bracket, to hold them in proper 
place. 

Porcelain knobs are made fast to the sticks with linen 
string or stout cotton line. Then an insulated copper wire 
is run through the holes in the knobs, and from the outer 
knob a rod of brass, copper, or German-silver, or even a 
piece of galvanized-iron lightning-rod, is suspended. Care 
should be taken to see that the joint between rod and wire 
is soldered so as to make perfect contact. Otherwise rust 
or corrosion will cause imperfect contact of metals, and in- 
terrupted vibrations would be the result. The upright stick 
should be ten or fifteen feet high, and may be attached to 
a house-top, a chimney, or on the corner of a barn roof. 

Another form of single antenna is shown in Fig. 16. 
This is a rod held fast in a porcelain insulator with cement. 
The insulator, in turn, is slipped over the end of a staff, or 
pole, which is erected on a building top or out in the open, 
the same as a flag-pole. Near the foot of the rod, and just 
above the insulator, a conducting-w4re is made fast and 
soldered. This is run down through porcelain insulators 
to the apparatus. 

If the pole is erected on a house-top it may be braced with 
wires, to stay it, but care must be taken not to have these 
wires come into contact with the rod, or conducting- wire. 

212 





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TYPES OP ANTENN/E 

2^3 



ELECTRICITY BOOK FOR BOYS 

Another form of antennae is shown in Fig. 17, where rods 
are suspended from a wire which, in turn, is drawn taut 
between two insulators. The insulators are held in a 
framework composed of two uprights and a cross-piece of 
wood. 

This frame may be nailed fast to a chimney and to the 
gable of a roof, as shown in the drawing ; and to steady the 
rods, so that they will not swing in a high wind, the lower 
ends should be tied together with cotton string, the ends of 
which should be fastened to the uprights. The leading-in 
wire is made fast to the top wire, from which the rods are 
suspended, and all the exposed joints should be soldered 
to insure perfect contact and conductivity. A modified 
form of the Marconi antennie is shown in Fig. 18. This is 
made of a metal hoop three of four feet in diameter held in 
shape by cross-sticks of wood, which can be lashed fast to 
the ring. Leading dow^n from it are numerous copper wires 
which terminate in a single wire, the whole apparatus re- 
sembling a funnel. The upper unions where the wires join 
the ring need not be soldered, but at the bottom, where they 
all come together and join the leading-in wire, it is quite 
necessary that a good soldered joint be made. This funnel 
may be hung between two upright poles on a house-top, or 
suspended from the towers or chimneys. 

Almost any metal plate will do for the ground, or the 
ground -wire (G W in Fig. 13) may be bound to a gas or 
water pipe which goes down deep in the ground, where it is 
moist. Rust or white lead in the joints of gas-mains some- 
times prevent perfect contact, but in water-pipes the cur- 
rent will flow readily through either the metal or the water. 

214 



LINE AND WIRELESS TELEGRAPHS 

To insure the most perfect results, it is best to have an in- 
dependent ground composed of metal, and connected direct- 
1}^ with the oscillator, or coherer, by an insulated copper 
wire. A simple and easily constructed ground is a sheet 
of metal, preferably copper, brass, or zinc, to the upper edge 
of which two wires are soldered, as shown in Fig. 19. This 
is embedded in the ground three or four feet below the sur- 
face. Another ground -plate is a sheet of metal bent in V 
shape and then inverted. Two wires are soldered to the 
angle, and the ends brought together and soldered. This 
ground is buried three or four feet deep, and stands in a 
vertical position, as shown at Fig. 20. At Fig. 21 a fiat 
ground is shown. This is a sheet of metal cut with pointed 
ends. The ground- wire is soldered to the middle of it, and 
it is then buried deep enough to be embedded in m.oist 
earth. 

One of the best grounds is an old broiler with a copper 
wire soldered to the ends of the handles, as shown at Fig. 
22. This is buried deep in the ground in a vertical position, 
and the insulated copper wire is carried up to the instru- 
ments. 

The most important part of the wireless telegraphic ap- 
paratus is now to be constructed, and this requires some 
care and patience. The coherer is the delicate, sensitive 
part of the apparatus on which hinges success or failure. 
There are various kinds of coherers designed and used by 
different inventors, but while the materials differ and the 
construction takes various forms, the same basic principle 
applies to all. 

The coherer can best be explained as a short glass tube 

215 



TiGf.ZO 




TiGpEZ 



TYPES OF GROUNDS 
2l6 



LINE AND WIRELESS TELEGRAPHS 

in which iron or other metalHc fihngs are enclosed. Corks 
are placed in both ends of the tube, and through these corks 
the ends of wire are passed, so that they occupy the position 
shown in Fig. 23, the ends being separated a quarter of an 
inch. Metal filings w411 not conduct an electric current 
the same as a solid rod or bar of the same metal, but resist 
the passage of current. 

After long periods of experimenting with various de- 
vices to detect the presence of feeble currents, or oscilla- 
tions, in the ether, the coherer of metal filings was adopted. 
When the oscillations surge through the resonator, the 
pressure, or potential, finally breaks down the air film 
separating the little particles of metal, and then gentty 
welds their sharp edges and corners together so as to form 
a conductor for the current. Before this process of co- 
hesion takes place these fine particles offer a very high 
resistance to the electrical energy generated by a dry cell 
or battery — so much so that no current is permitted to 
pass. But once the oscillations in the ether cause them to 
cohere — presto! the resistance drops from thousands of 
ohms to hundreds, and the current from the dry cell now 
flows easily through the coherer and deflects the needle 
of a galvanometer. This is the common principle of all 
coherers of the granulated metal type, although there are 
many modifications of the idea. 

The action of the electric and oscillatory currents on 
particles of metal can best be understood by placing some 
fine iron filings on a board, as shown at Fig. 24, and 
then inserting the aerial and ground wires in the filings, 
but separated by an eighth or a quarter of an inch. 

217 



ELECTRICITY BOOK FOR BOYS 

A temporary connection may be made as shown in 
Fig. 25. 

A A are aerials on both instruments; C is the open co- 
herer, or board with iron fihngs, in which the ends of the 
aerial and ground wires are embedded; D C is a dry cell; 






■FiGr23 




m25 



and R is a telegraphic relay, or sounder. If the wire across 
C was not parted and covered with filings, the dry cell 
would operate R, but the high resistance of the particles 
of metal holds back the current. 

On the opposite side, I C is the induction-coil ; K is the 

218 



LINE AND WIRELESS TELEGRAPHS 

telegraphic key, or switch, which makes and breaks the 
current; S B is the storage-batteries, or source of electric 
energy; and S G the spark-gap between the brass balls 
on the terminal rods. By closing the circuit at K the 
current flows through the primary of the induction-coil, 
affects the secondary coil, and causes a spark to leap across 
the gap between the brass balls. This instantly sets the 
ether in m^otion from A on the right, and the impulse is 
picked up by A on the left. This oscillation breaks down 
the resistance of the filings at C, and the current from bat- 
tery, or dry cell (D C), flows through the filings and operates 
the sounder, or relay (R). This operation takes place in- 
stantly, and the particles of metal are seen to cohere, or 
shift, so that better contact is established. But as soon 
as the spark has jumped across the gap the action of co- 
hesion ceases until the key (K) is again operated to close the 
circuit and cause another spark to leap across the gap. 
The shifting of the metal particles on the board (C) is what 
takes place in the glass tube of the coherer, Fig. 23, but in 
this confined space the particles will not drop apart again 
as on the flat surface, but will continue to cohere. A de- 
coherer is necessary, therefore, to knock the particles apart, 
so that the next oscillatory impulse will have a strong and 
individual effect. There are several forms of de-coherers 
in use, but for the amateur telegrapher an electric - bell 
movement without the bell, or, in other words, a buzzer 
with a knocker on the armature, will answer ever}^ purpose. 
(See description of buzzer on page 64.) It must be proper- 
ly mounted, so that on its back stroke, or rebound, the 
knocker will strike the glass tub^: and shake the particles of 

219 



ELECTRICITY BOOK FOR BOYS 

metal apart. For this purpose the vibrations of the arma- 
ture should be so regulated as to obtain the greatest pos- 
sible speed, in order that the dots and dashes (or short and 
long periods) will be accurately recorded through the co- 
herer and made audible by the sounder or telephone re- 
ceiver. 

Another form of coherer is shown in Fig 26. This is 
made of a small piece of glass tube, two rods that will ac- 
curately fit in the tube, some nickel filings, two binding- 
posts, and a base-block three inches and a half long. The 
two binding-posts are mounted on the block, and through 
the holes in the body of the posts the rods are slipped. 
They pass into the tube, and the bhmt ends press the small 
mass of filings together, as shown in the drawing. By 
means of the binding-posts these coherer-rods may be held 
in place and the proper pressure against the filings ad- 
justed; then maintained by the set -screws. The nickel 
filings may be procured by filing the edge of a five-cent 
piece. Obtain a few filings from the edge of a dime and 
add them to the nickel, so that the mixture will be in the 
proportion of one part silver to nine parts nickel. This 
mixture will be found to work better than the iron filings 
alone. The aerial and ground wires are made fast to the 
foot-screws of the binding-posts, and the base on which 
the coherer is mounted may be attached to a table or ledge 
on which the other parts of the receiving and recording 
apparatus are also installed. 

Another form of coherer is shown at Fig. 27. This is 
constructed in a somewhat similar manner to the one just 
described. A glass tube is provided with two corks having 

220 



LINE AND WIRELESS TELEGRAPHS 

holes in them to receive the coherer-rods. Two plugs of 
silver are arranged to accurately fit within the tube, and 
into these the ends of the coherer-rods are screwed or sol- 
dered. Between these silver plugs, or terminals, the filings 
of nickel and silver are placed, and the rods are pushed to- 
gether and caught in the binding-posts. The aerial and 
ground wires are made fast to the foot-screws of the posts. 

For long-distance communication it is necessary to have 
a condenser placed in series with the sparking or sending- 
out apparatus. (See the type of condenser described and 
-illustrated in chapter iv., page 72.) 

An astatic galvanometer is also a valuable part of the 
receiving apparatus, and the one described on page iii 
will show clearly the presence of oscillatory currents by 
the rapid and sensitive deflections of the needle. 

For local service, where a moderately powerful battery is 
employed, a telegraph-key, such as described on page 190, 
will answer very well, but for high-tension work, where a 
powerful storage-battery or small dynamo is employed, it 
will be necessary to have a non-sparking key, so that the 
direct current will not form an arc between the terminals 
of a key. Most of the keys used for wireless telegraphy have 
high insulated pressure-knobs, or the make and break is 
done in oil, so that the spark or arc cannot jump or be 
formed between the points. 

The plan of a simple non-sparking dry switch is shown at 
Fig. 28. This is built up on a block three inches wide and 
five inches long. It consists of a bar (A) , two spring inter- 
rupters (B and C), a spring (D), and the binding-posts (E E). 
They are arranged as shown in Fig. 28, and a front elevation 

221 



ELECTRICITY BOOK FOR BOYS 

is given in Fig. 29. The strip (B) lies flat on the block, and 
is connected with one binding-post by a wire attached under 
one screw-head and run along the under side of the base 
in a groove to the foot of the post. Strip C is of spring-brass, 
and is made fast to the base with screws. This is " dead," as 
no current passes through it, and its only use is to inter- 
rupt. The bar (A) is arranged as explained for the line tele- 
graph-key, and the remaining binding-post is connected to 
it by a wire run under the base and brought up to one of 
the angle-pieces forming the hinge. A high wood or por- 
celain knob is made fast at the forward end of the bar, so 
that when high-tension current is employed the spark will 
not jump from the bar to the operator's hand. The com- 
plete key ready for operation is shown at Fig. 30, and to 
make it permanent it should be screwed fast to the table, 
or cabinet, on which the coil and condenser rest. The plan 
of a '*wet" key is shown in Fig. 31, and the complete key 
in Fig. 32. 

A base of wood three by five inches is made and given 
several coats of shellac. Obtain a small rubber or com- 
position pill or salve box, and make it fast to the front end 
of the base with an oval-headed brass screw driven down 
through, the centre of the box. A wire leading to one bind- 
ing-post is arranged to come into contact with the screw, 
and the other post is connected by wire to one hinge-plate 
supporting the bar. The long machine screw, or rivet, 
passed dov/n through the knob and into the bar, extends 
down below the bar for half an inch or more, so that when 
the knob is pressed down the end of the screw, or rivet, will 
strike the top of the screw at the bottom of the box with- 

222 



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-fr 



W^ 



/A 



le® 



(D (^ j 



e(2> 



fw* 



TiG^za 




71(^30 



O ( 






Fi(^52 



"Fier.51 



DRY AND WET NON-SPARKING SWITCHES 
223 



ELECTRICITY BOOK FOR BOYS 

out the bar coming in contact with the edge of the box. 
When in operation the composition box is filled with olive 
oil or thin machinery oil, so that when contact is made by 
pressing the knob down the circuit will be instantly broken, 
the spring at the rear end of the bar drawing it back to rest. 
The oil prevents any sparks jumping across ; and also breaks 
an arc, should one form between the contact-points. With 
the addition of a good storage-battery (the strength of which 
must be governed by the size of the induction-coil and the 
distance the messages are sent) and a dry-cell or two for 
the receiving apparatus, the parts of the wireless apparatus 
are now^ ready for assembling. Full directions for making 
storage-cells is given in chapter ii., page 21, and for dry- 
cells in chapter ii., page 29. For short-distance work the 
plan shown in Figs. 33 and 34 will be found a very satis- 
factory form of apparatus. One of each kind of instrument 
should be at every point where communication is to be 
established. 

In the sending apparatus (Fig. 33) S C are the storage- 
cells, K the key, and I C the induction-coil. T T are the 
terminals and balls, S G the spark-gap, and P P the posts 
that hold the terminal rods. A W is the aerial wire run- 
ning up from one post, and G W the ground-wire connect- 
ing the other terminal post with the ground-plates. 

In the receiving apparatus (Fig. 34) C is the coherer, 
D C the de-coherer, T S the telegraphic sounder, or relay, 
and A G the astatic galvanometer. B is the dry-cell, or 
battery, and DCS the de- coherer switch, so that when 
the apparatus is not in use the dry-cell will not operate the 
buzzer or de- coherer. A W is the aerial wire and G W 

224 



1 



LINE AND WIRELESS TELEGRAPHS 



the ground-wire. Two or more storage-cells may be con- 
nected in series (that is, the negative of one with the posi- 
tive pole of the other) until a sufficiently powerful source 
of current is secured for the transmission of messages. 



AW 



W~\j(Sr nil 

a _^ 




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s.c. 



flGr.35 



GW. 



To operate the apparatus, the circuit is closed with K, 
and the current from S C flows around the primary coil in 



225 



ELECTRICITY BOOK FOR BOYS 

I C and affects the secondary coil, causing the spark to 
leap across the gap (S G) . This causes a disturbance through 
the wires A W and G W, and the ether waves are set in 
oscillatory motion from the antennae on the house-top. 
This affects the antennae at the receiving-point, and the im- 



"FiOr.54 




pression is recorded through the coherer (C) on the tele- 
graphic sounder or relay (T S), which is operated by the 
current from dry-cell or battery (B), since the oscillations 
have broken the resistance of the filings in the coherer (C) . 
The instant that the current passes through the coherer 

226 



LINE AND WIRELESS TELEGRAPHS 



AW 



CONDENSER 
? P 

oo 







TiGr55 



GW. 



and operates T S, the astatic galvanometer indicates the 
presence of current by the deflected needle. 

When the apparatus is in operation D C S is closed, so 
that the current from B operates the coherer (D C) . Direct- 

227 



ELECTRICITY BOOK FOR BOYS 

ly communication is broken off, the switch (D C S) should be 
opened; otherwise the buzzer would keep up a continuous 
tapping. For long-distance work a more efficient sending 
apparatus is shown in Fig. 35. This is composed of an in- 
duction-coil, with the terminal rods and brass balls form- 
ing the spark-gap, an oil key (K), and three or more large 
storage-cells, or a dynamo (if power can be had to run it). 
A condenser is placed in connection with the aerial and 
ground wires, so that added intensity or higher voltage is 
given the spark as it leaps across the gap. In operation 
this apparatus is similar to the one already described. 
Where contact is made with K the primary coil is charged, 
and by induction the current affects the secondary coil, the 
current or high voltage from which is stored in the con- 
denser. When a sufficient quantity is accumulated the 
spark leaps across S G and affects wires A W and G W. 
This action is almost instantaneous, and directly the im- 
pulse sets the ether in motion the same impulse is re- 
corded on the distant coherers and sounders. 

There are a great many modifications of this apparatus, 
but the principles are practically the sam^e, and while the con- 
struction of this apparatus is wdthin the ability of the aver- 
age boy, many of the more complicated forms of coherers 
and other parts would be beyond his knowledge and skill. 
Marconi has realized his ambition to send messages across 
the ocean without wdres, and is now doing so on a commer- 
cial basis, and at the rate of twenty-five words a minute. 
It is but the next step to establish communication half-way 
around the world, and finally to girdle the earth. 



Qiaptcr X 

DYNAMOS AND MOTORS 

TO adequately treat of dynamos and motors, a good- 
sized book rather than this single chapter would be 
necessary, and only a general survey of the subject is pos- 
sible. Its importance is unquestionable; indeed, the whole 
science of applied electricity dates from the invention of 
the dynamo. Without mechanical production of electric- 
ity there could be no such thing as electric traction, heat, 
light, power, and electro - metallurgy, since the chemical 
generation of electricity is far too expensive for commer- 
cial use. Surely it is a part of ordinary education now- 
adays to have a clear and definite idea of the principles of 
electrical science, and in no department of human knowl- 
edge has there been more constant and rapid advance. It 
is only a truism to assert that the school-boy of to-day 
knows a hundredfold more about electricity and its va- 
ried phenomena than did the scientists and philosophers of 
old — Volta and Galvani and Benjamin Franklin. Yet it 
was for these forerunners to open and blaze the way for 
others to follow. A beginning must always be made, and 
the Marconis and Edisons of to-day are glad to acknowledge 
their indebtedness to the experimenters and inventors of 
the past. And now to our subject. 

229 



ELECTRICITY BOOK FOR BOYS 

All dynamos are constructed on practically the same 
principle — a field of force rapidly and continuously cutting 
another fi.eld of force, and so generating electric current. 
The common practice in all dynamos and motors is to have 
the armature fields revolve within, or cut the forces of the 
main fields of the apparatus. There are many different 
kinds of dynamos generating as many varieties of current 
— currents with high voltage and low amperage; currents 
with low voltage and high amperage; currents direct for 
lighting, heating, and power ; currents alternating, for high- 
tension power or transmission, electro- metallurgy, and other 
uses. It is not the intention in this chapter to review all 
of these forms, nor to explain the complicated and intricate 
systems of winding fields and armatures for special purposes. 
Consequently^ only a few of the simpler forms of generators 
and motors will be here described , leaving the more complex 
problems for the consideration of the advanced student. 
For his use a list of practical text-books is appended in a 
foot-note.^ 

The Uni- direction Dynamo 

The uni-direction current machine is about the simplest 
practicable dynamo that a boy can make. It may be 
operated by hand, or can be run by motive power. The 
field is a permanent magnet similar to a horseshoe magnet. 
This must be made by a blacksmith, but if a large parallel 

^ First Principles of Electricity and Magnetism, by C. H. W. Biggs; 
The Dynamo: Hoiv Made and Used, by S. R. Bottone; Dynamo Electric 
Machinery, by Professor S. P. Thompson; Practical Dynamo Building for 
Amateurs, by Frederick Walker. 

230 



DYNAMOS AND MOTORS 



magnet can be purchased at a reasonable price so much the 
better, as time and trouble will be saved. This magnet 
should measure ten inches long and four inches and a half 
across, with a clear space seven inches long and one inch 
and three-quarters wide, inside measure. The metal should 
be half an inch thick and one inch and a quarter wide. A 
blacksmith will make and temper this magnet form ; then, 
if there is a power-station near at hand w^here electricity is 
generated for traction or lighting purposes, one of the work- 
men will magnetize it for you at a small cost; or it can be 
wound with several coils of wire, one over the other, and 
a current run through it. When properly magnetized it 
should be powerful enough to raise ten pounds of iron. 
This may be tested by shutting off the current and trying 
its lifting power. If the magnet is too weak to attract the 
weight the current should be turned on and another test 
made a few minutes later. 

Before the steel is tempered there should be four holes 
bored in the magnet and countersunk, so that screws may 
be passed through it and into the wooden base below, as 
shown at Fig. i. This wooden base is fourteen inches long, 
eight inches wide, and one inch in thickness. It may be 
made of pine, white-wood, birch, or any good dry w^ood that 
may be at hand. The blocks on which the magnet rests 
are an inch and a quarter square and seven inches long. 
The magnet is mounted directly in the middle of the base, 
an equal distance from both edges and ends, as shown in the 
plan drawing (Fig. lo). The blocks are attached with glue 
and brass screws driven up from the underside of the base. 

From a brass strip three-eighths of an inch wide and 

231 



ELECTRICITY BOOK FOR BOYS 

one -eighth of an inch thick cut a piece six inches long, 
and bore holes at either end through which long, slim, oval- 
headed brass screws may pass. Use brass, copper, or Ger- 
man-silver for this bar, and not iron or steel. To the under- 
side, and at the middle, solder or screw fast a small block of 
brass, through which a hole is to be bored for the spindle 
or shaft. This finished bar is shown in Fig. 2. When 
mounted over the magnet and held down with brass screws 
driven into the wood base, its end view will appear as 
shown in Fig. 3, A being the bar, B B the screws which hold 
it down, D the base into which they are driven, and C C 
the blocks under the magnet (N S). The object of this bar 
is to support one end of the armature shaft. From brass 
one-eighth of an inch thick bend and form two angles, as 
shown at Fig. 4. Two holes for screws are to be drilled in 
the part that rests on the base, and one hole, for the shaft 
to pass through, is bored near the top of the upright plate. 
The centre of this last hole must be the same height from 
the base as is the hole in the bar (Fig. 2) when mounted 
over the magnet, as shown at Fig. 3. The location of these 
plates is shown in the plan (Fig. 10). There is one plate at 
each end of the base, as indicated at B and B B, the shaft 
passing through the hole in the brass block at the under- 
side of the bar (C). These angles are the end-bearings for 
the armature shaft, and should be accurately centred so 
that the armature will be properly centred between the N 
and S bars of the magnet. 

The armature is made from soft, round iron rod one inch 
and a half in diameter and five inches long. A channel is 
cut all around it, lengthwise, five-eighths of an inch wide 

232 




(^ 



7I&3- 



lT\CrA 



Fie-.9., 




TV^.J 




Fig-. 5. 



DETAILS OF UNI-DIRECTION DYNAMO 
233 



ELECTRICITY BOOK FOR BOYS 

and half an inch deep, as shown in Fig. 5. This will have 
to be done at a machine-shop in a short bed-planer, since 
it would be a long and tedious job to cut it out mth a 
hack-saw. The sharp corners should be rounded off from 
the central lug, so that they will not cut the strands of fine 
wire that are to be wound round it. 

Two brass disks, or washers, are to be cut, one inch and 
a half in diameter and from one-eighth to one-quarter of 
an inch thick, for the armature ends. A quarter-inch hole 
is to be made in the centre of each for the shaft to fit in, and 
two smaller holes must be drilled near the edge, and oppo- 
site each other, so that machine-screws may pass through 
them and into holes bored and threaded in the ends of the 
armature, as shown at Fig. 5. These ends will appear as 
shown at Fig. 6, and the middle hole should be threaded so 
as to receive the end of a shaft. When the shaft is screwed 
in tight the end that passes through the brass disk must 
be tapped with a light hammer to rivet the end, and so 
insure that the shaft will not unscrew. 

The shafts should be of hard brass or of steel. The one 
at the front should be one inch and a half in length, and 
that at the rear six inches long, measuring from the outer 
face of the brass end to the end of the shaft. From box- 
wood or maple turn a cylinder three-quarters of an inch in 
diameter and an inch long, with a quarter-inch hole through 
it. Over this slip a piece of three-quarter- inch brass or 
copper tubing that fits snugly, and at opposite sides drill 
holes and drive in short screws that will hold the tube fast 
to the hub. They must not be so long as to reach the hole 
through the centre. Place this hub in a vise, and with a 

234 



DYNAMOS AND MOTORS 



hack-saw cut the tube across in two opposite places, so 
that you will have the cylinder with two half -circular shells 
or commutators screwed fast to it, as shown at Fig. 7. 
This hub will fit over the shaft at the front end of the 
armature, and will occupy the position shown at F in 
Fig. 10. 

Cut two small blocks of wood for the brushes and bind- 
ing-posts, and bore a hole through them, so that the foot- 
screw of a binding-post may pass through the block and 
into the post, as shown at Fig. 8. From thin spring copper 
cut a narrow strip and bend it over the block, catching it at 
the. top with a screw and lapping it mider the binding-post 
at the outside. 

From boxwood or miaple have a small wooden pulley 
turned, with a groove in it and a quarter-inch hole through 
the centre. This pulley should be half an inch wide and 
one inch and a half in diameter, as show^n at Fig. 9. This 
is to be attached at the end of the long shaft, where it will 
occupy the position shown at E in Fig. 10. 

All the parts are now ready for assembling except the 
armature, which must be wound. Before laying on the 
turns of wire the channel in the iron must be lined with 
silk, held in place with glue or shellac. A band of silk 
ribbon is given two turns about the centre of the iron, and 
the sides are so completely covered with silk that not a 
single strand of wire w^ill come into direct contact with the 
iron. Great care must be taken, when winding on the 
wire, not to kink, chafe, or part the strands. The channel 
should be filled but not overcrowded, and when full several 
wraps of insulating tape should be made fast about the 

235 



\(D ^ 



®fl® 





® 



N 



, .1 — inpnr-r— T. . 



TlGr.lO, 



a A t 



PLAN OF THE UNI-DIRECTION DYNAMO 



236 



DYNAMOS AND MOTORS 



armature to hold the wire firmly in place and prevent it 
from working out at the centre when the armature is driven 
at high speed. The armature, when properly wound and 
wrapped, will appear as shown at A in Fig. ii, and it is 
then ready to have the ends screwed on. Several sizes of 
wire may be used to wind the armature, according to the 
current desired, but for general use it would be well to use 
No. 30 silk-insulated copper wire. 

About four ounces should be enough for this armature, 
and the ends are to be passed through small holes in the 
brass end (B) ; see Fig. 11. One end must be soldered to 
one commutator, the other end to the other commutator. 
The end-piece (B) is attached to the iron armature (A) with 
machine -screws; then C is to be made fast in a similar 
manner. 

When putting the parts together, it would be well to use 
some shellac on the wooden cylinder and driving-wheel to 
make them hold to the shaft. 

By following the plan in Fig. 10, it will be an easy matter 
to put the parts together; when they are assembled the 
complete machine will appear as shown in the drawing 
(Fig. 12). 

The driving-wheel should be of wood five-eighths of an 
inch thick and six inches in diameter, and held in the frame 
of wood and metal brackets by a bolt. A short handle can 
be arranged with which to turn the wheel, and a small 
leather belt will transmit the power to the small wheel on 
the armature shaft. As the armature is revolved the lines 
of force are cut and the current is carried out through the 
wire attached to the binding-posts on the blocks (G G), 

237 



ELECTRICITY BOOK FOR BOYS 

Considerable current may be generated if the armature 
is driven at higher speed than the hand- wheel will cause it 
to revolve. This can be accomplished by running the belt 




TlQr.iZ 



over a larger wheel, such as the fly-wheel of a sewing-ma- 
chine, or connecting it to a large pulley on a water-motor. 
The latter may be attached to a faucet in the wash-tub if 
there is pressure enough to do the work. 

238 



DYNAMOS AND MOTORS 



A Small Dynamo 

All dynamos are constructed on the same general prin- 
ciple as that of the uni - direction machine just described; 
but they differ in their windings, the quantities of metal 
electrified, the sizes and lengths of wire wound on both 
armature and field, and in their shape and speeds. 

In large dynamos it is impossible to employ steel mag- 
nets of the required size. In place of them soft iron cores 
are used and magnetized by external electric current; or 
the wiring is done in "series" or "shunt," so that the fields 
will be self - exciting once the machine has been properly 
started. 

The principal difference in dynamos is, perhaps, more 
clearly illustrated by the diagrams shown in Figs. 13, 14, 
15, and 16. In Fig. 13 the arrangement of armature and 
field-magnet is the same as in the uni-direction machine, 
the field (F) being of magnetized steel, while the armature 
(A) is of soft iron wound with coils of fine wire, the ends 
of which are brought out at the commutators (C), through 
which the current is carried to the brushes (B and B B) . If, 
however, the soft iron cores are used, a separate magnetiz- 
ing electric current must be passed through the coils of wire 
wound about the field-pieces, so that they will become tem- 
porary magnets — the same as the cores of an electric bell 
movement, a telegraph-sounder, or the induction-coil core 
when a current is passed through the primary coil. The 
armature (A) is then driven at high speed by power, and 
the current is taken off for use through wires that lead 
from B and B B. 

239 



ELECTRICITY BOOK FOR BOYS 

In all of these figures the armatures rotate, in the space 
between the large pole-pieces of the field-magnets, in the 
same direction as the hands of a clock move. In these fig- 
ure drawings the field-magnets, commutators, and brushes 
only are shown, the armature being indicated by the cir- 
cle (A). 

Figure 13 represents a dynamo, the field - magnets of 
w^hich are excited by a separate battery or generator. 
This is known as a "separately excited" machine, and is 
employed for various uses. The brushes (B and B B) are 
connected to the external circuit — that is, with the motor 
or other apparatus for which current is to be generated. 
The magnetic field in which the armature rotates will be 
constant if the exciting current is constant, like the mag- 
netism in the magnet of the uni-direction current machine. 

The induced electro-motive force (which depends upon 
the rate at which the lines of force are cut) will be constant 
for the given speed at which the armature rotates. This 
action is the same as that described for the uni-direction 
current machine. 

Figure 14 is the diagram of a "series "-wound dynamo. 
The field and armature are soft gray iron, and are wound 
in series — that is, one end of the magnet-winding is made 
fast to the brush B, the other to the brush B B, and the 
apparatus to be operated by the current is let in between 
B B and the magnet, as shown by the indicated electric arc- 
light in the illustration. The field-magnet coils, the arma- 
ture, and the external conductors are in series with each 
other, forming a simple circuit. When the armature is 
driven at high speed the field-magnets become self -exciting, 

240 



DYNAMOS AND MOTORS 



with the result that current is generated. Its simple course 
is through B B to commutators on the hub, thence through 
one winding on the iron armature A, to B, through field 
F, and back to B B again, operating in its course any pieces 
of equipment designed for electric impulse, such as motors, 
or lamps, trolley-cars, trains, or electric machinery. 

The third type, shown in Fig. 15, is known as " shunt "- 
winding. The field -magnet coils and the external resist- 









ance are in parallel, or shunt with each other, instead of in 
series. The brushes are connected with the external cir- 
cuit, and also with the ends of the field-magnet coils. This 
is clearly shown in the drawing. The ends of the field- 
coils are connected with brushes B and B B, and the ex- 
ternal circuit wires are connected also with the same brushes, 
and pass down to such an apparatus as a plating bath, in 
which the current runs through the electrode, the electro- 
lyte, and the cathode, most of the current generated passing 
16 241 



ELECTRICITY BOOK FOR BOYS 

through the external circuit. The field-coils are of fine wire, 
and when the armature is rotated there will always be a 
current through the field - magnets, whether the external 
circuit is complete or not. If a break occurs in the exter- 
nal circuit, a more powerful current will consequently pass 
through the field-magnets. 

In Fig. i6 a *' compound "-wound dynamo is shown. It is 
a combination of the series and the shunt machine. The 
field-magnet coils are composed of two sizes of wire. There 
are comparatively four turns of stout wire and many turns 
of fine wire, the ends of both being connected, as shown in 
the drawing. The stout wire leads out to lamps which are 
arranged in series, as shown at the foot of the drawing. 
The current developed by this dynamo is one of "constant 
potential," and is used almost exclusively for incandescent 
lamps, the "constant" current from the series-wound ma- 
chine being used for arc-lamps, power, and other commer- 
cial purposes. 

It will not be necessary to use the first or last systems, nor 
to experiment with the alternating current, with its phases 
and cycles. All that a boy wants is a good direct-current 
machine that will light lamps, run sewing-machines or mo- 
tors, and furnish the power for long-distance wireless teleg- 
raphy and other apparatus requiring considerable current. 

To begin with, it would be better to make a small dynamo 
and study its principles as you progress; then it will be a 
great deal easier to construct a larger one. It will be neces- 
sary to have the iron parts made at a blacksmith -shop, 
since the various cutting, threading, and tapping operations 
call for the use of special iron-working tools. Soft iron 

242 



DYNAMOS AND MOTORS 



should be used, and if a piece of cast-iron can be procured 
for the lugs or magnet ends it will give better service than 
wrought-iron. 

From three-quarter-inch round iron cut two cores, each 
three inches and a half long, and thread them at both ends, 
as shown at B B in Fig. 17. From band-iron five-eighths 
of an inch thick and one inch and a half wide cut a yoke (A) , 
and bore the indicated holes two inches and three-quarters 
apart, centre to centre. These should be threaded so that 
the cores (B B) will screw into them. From a bar of iron 
cut off two blocks one inch and a half by one inch and a 
half by two inches for the lugs. Now, with a hack-saw 
and a half-round file, cut out one side of each lug, as shown 
at C. These lugs are to be bored and threaded at one end, 
so that they can be screwed on the lower ends of the cores 
(CC). 

For a larger dynamo the yoke should be made six inches 
long, one inch thick, and two inches and a half wide. The 
cores should be of one-inch iron pipe. These will be hollow, 
as shown at B B in Fig. 18. For the ends cast-iron blocks 
must be made or cast from a pattern two inches and three- 
quarters square and four inches high, as shown at C. The 
yoke (A) and the lugs (C) are bored and threaded to receive 
the one-inch pipe, and when set up this will constitute an 
iron field-magnet six inches wide, two inches thick, and 
nine inches high. This, if properly wound, should develop 
a quarter of a horse-power. 

The parts shown in Fig. 17, when screwed together, will 
give you a field-magnet two by one and a half by five and 
three-quarter inches high, and will appear as shown in Fig. 

243 



ELECTRICITY BOOK FOR BOYS 

19, A being the yoke at the top, B B the cores, C C the 
lugs, and D a strip of brass screwed fast across the back of 
the lugs (C C) , and in which a hole is bored to act as a bear- 
ing for one end of the armature shaft. Between the lugs 
and the strip (D) fibre washers three-eighths of an inch in 




TIG-.I5 



fiGr.iq. 



riG-.2Q 



»'l >ll» D IP' i ' 







}■ 


;'T I " "" " '^ ^ 


E E. 

G- 
or-' 



FiQ^;^L 



thickness are placed to keep the strip away from the lugs. 
A hole is bored directly through the middle of each lug, 
from front to rear, and it is threaded at each end so that 
a machine-screw will fit in it. The brass strip (D) is five- 
eighths of an inch wide, three-sixteenths of an inch thick, 
and four inches long. Copper or German -silver may be 
used in place of brass, but iron or steel must not be em- 
ployed, since these metals are susceptible to magnetism. 

244 



DYNAMOS AND MOTORS 



Two holes should be made in the bottom of each lug, and 
threaded, so that machine-screws may be passed through a 
wooden base and into them in order to hold the dynamo on 
the base. 

Figure 20 is an end view of the field-magnets showing the 
yoke at A, the core at B, the lug at C, and the bearing and 
binding-strip of yellow metal at D. Two blocks of hard- 
wood, an inch square and one inch and a half long, are cut 
and provided with holes, so that they can be fastened to the 
lugs C C with long, slim machine-screws, as shown at E E 
-in Fig. 21. This is a view looking down on the magnets, 
blocks, and straps. These blocks are to support the brushes 
and terminals, and should be linked across the face with a 
brass strap G, so that the other end of the armature shaft 
may be supported. Care must be taken, when setting straps 
D and G, to have them line. The holes, too, must be cen- 
tred, since the armature must revolve accurately within 
the field-lugs (C C) without touching them, and there is but 
one-sixteenth of an inch space between them. 

From hard -wood half an inch in thickness cut a base, 
six by seven inches, and two strips an inch wide and five 
inches long. With glue and screws driven up from the 
underside of the strips fasten them to the base, as shown 
at Fig. 22. Then make the field-magnets fast to the base 
with long machine-screws, using washers under the heads 
at the underside of the base-board. The mounting should 
then appear as shown in Fig. 28. 

From steel, half an inch in diameter, cut a shaft five 
inches long. Have it turned down smaller at one end for 
three-eighths of an inch, and at the other end for a distance 

245 



ELECTRICITY BOOK FOR BOYS 




of one inch and a half, as shown at Fig. 23. This is for the 
armature, and it should fit between D and G in Fig. 21, 
and should revolve easily in the holes cut to receive it in 
both straps, with not more than one-eighth of an inch 
play forward or backward. The long, projecting end should 

246 



DYNAMOS AND MOTORS 



be at the rear, and should extend beyond strip D for three- 
quarters of an inch, so that the driving-pulley can be made 
fast to it. 

The armature is made up of segments or laminations of 
soft iron and insulated copper wire. The laminated arma- 
ture works much better than does the solid metal ring or 
lug, and a pattern may be made from a piece of tin from 
which all the sections can be cut. With a compass, strike a 
two-inch circle on a clear piece of tin; then mark it off, as 
shown at Fig. 24, and cut it out with shears. The hole at 
the centre of the pattern need not be bored, but a small 
pinhole should be made so that a centre-punch can be used 
to indicate the middle of each plate for subsequent per- 
foration. Ordinary soft band iron may be employed for 
this purpose, and the sections should not be more than one- 
sixteenth of an inch in thickness. 

It will take some time to cut out the required number of 
pieces for this small armature. When they are all residy 
they should be slipped over the shaft, and if they have been 
properly matched and cut, they should appear as a solid 
body, one inch and a half long. 

Arrange these laminations on the armature shaft so that 
when the shaft is in position the mass of iron v/ill be within 
the lugs of the field-magnets. The holes through the iron 
plate should be so snug as to call for some driving to put 
them in place. Each disk of iron should be given a coat of 
shellac to insulate it, and between each piece there should 
be a thin cardboard or stout paper separator to keep the 
disks apart. These paper washers should be dipped in hot 
parafhne, or thick shellac may be used to obtain a good 

247 



ELECTRICITY BOOK FOR BOYS 

sticking effect and so solidify the laminations into a com- 
pact mass. When this operation is completed the amiature 
core should appear as shown in Fig. 25. 

From maple, or other hard- wood with a close grain, make 
a cylinder three-quarters of an inch long and one inch in 
diameter to fit the shaft. Over this drive a piece of copper 
or brass tubing, and at four equal distances, near the rear 




riQr.29., 



riGr.30. 



248 



DYNAMOS AND MOTORS 



or inner edge, make holes and drive small, round-headed 
screws into the wood. Then, with a hack-saw, cut the tube 
into four equal parts between the screws. This is the 
commutator. In order to hold the quarter circular plates 
fast to the cylinder, remove one screw at a time, and place 
thick shellac on the cylinder. Then press the plate firmly 
into place and reset the screw. Repeat this with the other 
three, and the armature will be ready for the winding. 

The voltage and amperage of a dynamo is reckoned by 
its windings, the size of wire, the number of turns, and the 
direction. This is a matter of figuring, and need not now 
concern the young electrician, since it is a technical and 
theoretical subject that may be studied later on in more 
advanced text-books. 

For this dynamo use No. 22 cotton-insulated copper wire 
for the armature, and No. 16 double cotton-insulated cop- 
per wire for the field. The armature, when properly wound 
and ready for assembling with the brushes and wiring, will 
appear as shown in Fig. 26. 

A small driving-wheel two inches in diameter and half 
an inch thick must now be turned from brass and provided 
with a V-shaped groove on its face. The hub, at one side, 
is fitted with a set-screw, so that it can be bound tightly on 
the shaft. This ptilley is made fast to the shaft at the rear 
of the dynamo, and on the opposite end to where the com- 
mutator hub is attached. 

A diagram of the wiring is shown in Fig. 29, and in Fig. 
30 the mode of attaching the ends of the coil wires to the 
commutators is indicated. Two complete coils of wire 
must be made about each channel of the armature, as illus- 

249 



ELECTRICITY BOOK FOR BOYS 



trated on the drum of Fig. 30. These are separated by a 
strip of cardboard dipped in paraffine and placed at the 
centre of a channel while the winding is going on. In some 
armatures the coils are laid one over the other; but with 
this construction, and in the case of a short-circuit, a broken 
wire, or a burn-out, it is impossible to reach the under coil 
without removing the good one. 

Begin by attaching one end of the fine insulated wire to 
commutator No. i ; then half fill the channel, winding the 
wire about the armature, as indicated in Fig. 30. When 
the required number of turns has been made, carry the end 
around the screw in commutator No. 2, baring the wire to 
insure perfect contact when caught under the screw-head. 
From No. 2 carry the wire around through the channel at 
right angles to the first one, and after half filling it bring 
the end out to commutator No. 3. Carry the wire in again 
and fill up the other half of the first channel, and bring the 
end out to commutator No. 4. Fill up the remaining half 
of the second channel; then attach the final end to com- 
mutator No. I, and the armature winding will be complete 
without having once broken the strand of wire. 

To keep the coils of wire in place, and to prevent them 
from flying out, under the centrifugal force of high speed, 
it would be well to bind the middle of the armature with 
wires or adhesive tape. 

After driving down the small screws over the leading- 
in and leading -out wires the armature will be ready to 
mount in the bearings. As the blocks that support the 
brushes and binding - posts partly close the opening to 
the cavity at the front, the armature will have to be in- 

250 



DYNAMOS AND MOTORS 



serted from the back into the strip (G) in Fig. 21. Then 
the back strip (D) is screwed in place. The armature, when 
properly mounted, should revolve freely and easily within 
the field-lugs without friction, and the lugs must by no 
means touch the armature. From thin spring -copper 
brushes may be cut and mounted on the block under the 
binding-posts, so that one will rest on top of the commuta- 
tors while the other presses up against the underside. The 
wiring is then to be placed on the field-magnets. This is 
carried out as described for the electric magnets on pages 
54-58 of chapter iv., each core receiving five or seven layers, 
or as much as it will hold without overlapping the lug or 
yoke. The ends of the wires are connected as shown at 
Fig. 14 or Fig. 15, the ends being carried down through the 
base and up again in the right location to meet the foot of 
a binding-post. The complete dynamo will appear as 
shown in Fig. 28. 

Before the dynamo is started for the first time it would 
be well to run a strong current through the field coils. 
The residual magnetism retained by the cores and iron parts 
will then be ready for the next impulse when the dynamo 
is started again. Larger dynamos may be made of this 
type. With an armature, the core of which is four inches 
in diameter and six inches long, having eight instead of 
four channels, and placed within a field of proportionate 
size, the dynamo will develop one horse-power. 

A Split-ring Dynamo 

Another type of dynamo is shown in Fig. 31. This is 
composed of a wrought or cast iron split-ring wound for the 

251 



ELECTRICITY BOOK FOR BOYS 

field, an armature made up of laminations, and the neces- 
sary brushes, posts, commutators, and wire. 

Have a blacksmith shape an open ring of iron, in the form 
of a C, three-eighths of an inch thick and four inches wide. 




The opening should be three inches wide, as shown in Fig. 
32. This ring should measure five inches on its outside 
diameter, and the ends are to be bored and threaded to 

252 



DYNAMOS AND MOTORS 



receive machine - screws. Two lugs are to be made from 
wrought-iron to fit on these ends. These should be four 
inches long, an inch and a half high, and three-quarters of 
an inch thick at top and bottom. They should be hollowed 
out at the middle, so that an armature two inches in di- 
ameter will have one -eighth of an inch play all around 
when arranged to revolve within them. Holes are made 
through the lugs to receive machine-screws, which are driven 
into the holes in the ends of the iron (C). Wrought-iron L 
pieces are made one inch and a half high and an inch across 
-the bottom, and with machine-screws they are made fast to 
the backs of the lugs to act as feet on which the field-mag- 
net may rest, as shown in Fig. 33. Across the back of the 
lugs, and set away from them by fibre washers, a strap of 
brass is made fast. This measures three-quarters of an 
inch wide and a quarter of an inch thick, and at the middle 
of it a three-eighth-inch hole is bored to receive the rear 
end of the armature shaft. This is shown in Fig. 34, which 
is a front view of the. field, or C, iron, the lugs (L L) and 
feet (F F) , the armature bearing (S) , and the base (B) , of three- 
quarter-inch hard- wood. The field-magnet is bolted to the 
base with lag-screws, so that it will be held securely in place. 
The laminations for the armature core are two inches in 
diameter, and are cut from soft iron one -sixteenth of an 
inch thick. They have eight channels, as shown in Fig. 35, 
and the tubing on the commutator hub is divided into four 
parts so that the terminals from each coil can be brought 
to a commutator, as described for Fig. 30. In the eight- 
channel armature, however, there is but one coil of wire in 
each channel. 

253 




B 



■ffl 



1^ 



TI&--36. 



r 




ri&35 





TlGr57 




ri&55. 



DETAILS OF SPLIT-RING DYNAMO 



DYNAMOS AND MOTORS 



In Fig. 36 a plan of the armature is shown, S representing 
the shaft, B B the bearings, L the laminations, C the com- 
mutators and hub, P the driving- pulley, and N N the nuts 
that hold the laminations together and lock them to the 
shaft. The shaft is half an inch in diameter, the lamina- 
tions four inches thick, and the commutator barrel one inch 
in diameter and three-quarters of an inch long. The shaft 
is turned down from the middle to where P and C are at- 
tached; then at the front end it is made smaller, where it 
passes through the front bearing. 

With the detailed description already given for the con- 
struction of the small dynamo, it should be an easy matter 
to carry out the work on this one, and a quarter horse-power 
generator should be the result. The field-magnet is wound 
with five or seven layers of No. 16 double cotton-insulated 
wire, and the armature with No. 22 silk or cotton-covered 
wire. The connections may be made for either the series 
or the shunt windings shown in Figs. 14 and 15. Another 
type of field is shown in Fig. 37, where two plates of iron are 
screwed to one core, and the lugs are, in turn, made fast to 
the inner sides of the plates within which the armature re- 
volves. The "Manchester" type is shown in Fig. 38, where 
two cores, constructed by a top and bottom yoke, are ex- 
cited by the coils, and the lugs are arranged between the 
cores, so that the armature revolves within them. 

A Small Motor 

The shapes, types, powers, and forms of motors are as 
varied and different as those of dynamos, each inventor 

255 



ELECTRICITY BOOK FOR BOYS 

designing a different type and claiming superiority. The 
one common principle, however, is the same — ^that of an 
armature revolving within a field, and lines of force cutting 
lines of force. A motor is the reverse of a , dynamo. In- 
stead of generating current to develop power or light, a 
current must be run through a motor to obtain power. 

Motors are divided into two classes: the D C, or di- 
rect current, and the A C, or alternating current. For the 
amateur the direct-current motor will meet every require- 
ment, and since the battery, or dynamo current, that may 
be available to run a motor, is in all probability a direct 
one, it will be necessary to construct a motor that is adapted 
to this source of powder and for the present avoid the com- 
plications of the alternating current both in generation and 
in use. 

The direct-current motor is an electrical machine driven 
by direct current, the latter being generated in any desired 
way. This current is forced through the machine by electro- 
motive force, or voltage ; the higher the pressure, or voltage, 
the more efficient the machine. Be careful lest too much 
current (amperage) is allowed to flow, for the heat developed 
thereby will burn out the wiring. 

Motors are so constructed that when a current is passed 
through the field and armature coils the armature is ro- 
tated. The speed of the armature is regulated by the 
amount of amperage and voltage that passes through the 
series of magnets, and this rotating power is called the 
torque. 

Torque is a twisting or turning force, and when a pul- 
ley is made fast to the armature shaft, and belted to con- 

256 



DYNAMOS AND MOTORS 



nect with machinery, this torque, or force, is employed for 
work. 

The speed of an armature when at full work is usually 
from twelve hundred to two thousand revolutions a minute. 
As few machines are designed to work at that velocity, a 
system of speeding down with back gears, or counter-shafts 
and pulleys, is employed. The motor itself cannot be slowed 
down without losing power. The efhciency of motors is due 
to the centrifugal motion of the mass of iron and wire in the 
armature and the momentum it develops when spurred on 
by the magnetism of the field-magnets acting upon certain 
electrified sections of the armature. The armature of a 
working motor is usually of such high resistance that the 
current employed to run it would heat and burn out the 
wires if the full force of the current was permitted to flow 
through it for any length of time. As the armature rotates 
it has counter electro-motive force impressed upon it. This 
acts like resistance, and reduces the current passing through. 
The higher the speed the less current it takes, so that after 
a motor has attained its highest, or normal speed, it is using 
less than half the current required to start it. 

Reduction of current in the armature reduces torque, so 
that the turning force of the armature is reduced as its 
speed of rotation increases. On the other hand, the mo- 
mentum, or "throw," produces power at high speed, to- 
gether with an actual saving of current. An armature re- 
volving at sixteen hundred revolutions, and giving half a 
horse-power on a current of five amperes, is more economi- 
cal than one making three to five hundred revolutions, and 
giving half a horse-power on a current of fifteen to twenty 
17 257 



ELECTRICITY BOOK FOR BOYS 

amperes. Thus, a slowly turning armature takes more cur- 
rent and exerts higher torque than a rapidly rotating one. 
To protect the fine wire on the armature from burning, 
in high-voltage machines a starting-box, or rheostat, is em- 
ployed. The motor begins working on a reduced current, 
and as it picks up speed more current is let in, and so on 
until the full force of the current is flowing through the 
motor. It is then turning fast enough to protect itself 
through the counter electro-motive force. This can be 
understood better after some practical experience has been 
had in the construction and running of motors. Of the 
various form.s of motors but three will be illustrated and 
described; but the boy with ideas can readily design and 
construct other types as he comes to need them. 

The Flat-bed Motor 

The simplest of all motors is the flat-bed type, illustrated 
in Fig. 39. This is composed of a magnet on a shaft re- 
volving before a fixed magnet attached to the upright board 
of the base. Where space is no object, this motor will 
develop considerable power from a number of dry-cells or 
a storage-battery. Now, in the section relating to dyna- 
mos, four different systems of wiring were shown. In 
motors of the direct - current type but one system will be 
described — that of the series-winding, illustrated in Fig. 40. 
The current, entering at A, passes to the brush (B) , thence 
through the commutator (C) and the armature coils. It 
runs on through the brush (B B), the field-coils (F), and out 
at D. This is the same course the current takes in the 

258 




Ti<x4l. 



I TIG-^O 13 





7lG:39. 



A FLAT-BED MOTOR AND PARTS 



ELECTRICITY BOOK FOR BOY S 

series- wound dynamo illustrated in Fig. 14, page 241, and 
with such a dynamo current could be generated to run any 
series-wound, direct-current motor. 

From hard-wood half an inch thick cut a base-piece six 
inches and a half long by three inches and a half wide. 
Arrange this base on cross-strips three-quarters of an inch 
wide and half an inch thick, making the union with glue 
and screws driven up from the underside. To one end of 
this base attach an upright or back two inches and three- 
quarters high, and allow the lower edge to extend down to 
the bottom of the cross-strip, as shown at the left of Fig. 
39. Make this fast to the end of the base and side of the 
cross-strip with glue and screws; then give the wood a 
coat of stain and shellac to properly finish it. 

Now have a blacksmith make two U pieces of soft iron 
for the field and armature cores, as shown in Fig. 41. These 
are of quarter-inch iron one inch and a half in width. 
They are one inch and three-quarters across and the sam.e 
in length. One of them should have a half -inch hole bored 
in the end (at the middle), and above and below it smaller 
holes for round-headed screws to pass through. By means 
of these screws the U is held to the wooden back. The 
other U is to have a three-eighth-inch hole bored in it so 
that it will fit on the armature shaft. Wind the U irons 
with six layers of No. 20 cotton-insulated wire, having first 
covered the bare iron with several wraps of paper. Use 
thick shellac freely after each layer is on, so that the turns 
of wire will be well insulated and bound to each other. 
Follow the wiring diagram shown in Fig. 40 when winding 
these cores, and when the field is ready, make it fast to 

260 



DYNAMOS AND MOTORS 



the back with three - quarter - inch round-headed brass 
screws. 

Directly in the middle of the hole through the field iron 
bore a quarter-inch hole for the armature shaft to pass 
through; then make an L piece, of brass, two inches high, 
three-quarters of an inch wide, and with the foot an inch 
long, as shown at Fig. 42. Two holes are made in the foot 
through which screws will pass into the base, and near the 
top a quarter-inch hole is to be bored, the centre of which 
is to line with that through the back, at the middle of the 
field core. The shaft is made from steel three-eighths of an 
inch in diameter and six inches and a half long. One inch 
from one end the shaft should be turned down to a quarter 
of an inch in diameter, and one inch and a quarter from the 
other end it must be reduced to a similar size. The short 
end mounts in the back and the long one receives the pulley, 
after the latter passes through the L bearing. A piece of 
three-eighth-inch brass tubing an inch long is slipped over 
the shaft two inches from the pulley end and secured with 
a flush set-screw. This tubing is then threaded and pro- 
vided with two nuts, one at either end, so that when the 
armature U is slipped on the collar the nuts can be tightened 
and made to hold the magnet securely on the shaft. This 
shaft is clearly shown in the sectional drawings Fig. 43. 

At the left side the shaft (S) passes into the wood back 
through the quarter-inch hole. At the outside a brass 
plate with a quarter-inch hole is screwed fast and acts as 
a bearing. The shaft does not touch the field -magnet 
(F M) , because the hole is large enough for the quarter-inch 
shaft to clear it. A fibre washer (F W) is placed on the 

261 



ELECTRICITY BOOK FOR BOYS 

shaft before it is slipped through the back. This prevents 
the shaft from playing too much, and deadens any sound of 
** jumping" while rotating. 

At the middle the shaft (S) passes through the brass col- 
lar on which the threads are cut. A M represents the arma- 
ture magnet, and W W the washers and nuts employed to 
bind it in place. At the right, S again represents the shaft, 
B the bearing, C the commutator hub, and P the pulley, 
while R is the small block under the hub to which the 
brushes and binding-posts are attached. 

From the descriptions already given of dynamos, and 
with these figure drawings as a guide, it should be an easy 
matter to assemble this motor. 

The ends of the field and armature magnets should be 
separated an eighth of an inch. The hub for the commu- 
tators is three-quarters of an inch long and three-quarters 
of an inch in diameter. The commutators are made as de- 
scribed for the uni-direction current machine, care being 
taken to keep the holding screws from touching the shaft. 
A three-quarter-inch cube of wood is mounted on the base, 
under the commutator hub, and to this the brushes and 
binding-posts are made fast, as shown in Fig. 39. Unless 
the armature happens to be in a certain position this motor 
is not self -starting, but a twist on the pulley, as the current 
is turned on, will give it the necessary start. Its speed will 
then depend on the amount of current forced through the 
coils. 

Another Simple Motor 

Another type of motor is shown in Fig. 44, where one 
field-winding magnetizes both the core and the lugs. The 

262 



DYNAMOS AND MOTORS 



frame of this motor is made up of two plates of soft iron a 
quarter of an inch thick, six inches long, and two inches and 
a half wide. Each plate is bent at one end so as to form 
a foot three-quarters of an inch long, and a half- inch hole is 
drilled one inch and a quarter up from the bottom, at the 
middle of each plate. Through this hole pass the machine- 
screws which hold the iron core in place between the side- 
plates. The core is made of three-quarter-inch round iron 
two inches and three-quarters long, and drilled and thread- 
ed at each end to receive the binding machine-screws. 

. Two lugs are cut from iron, and hollowed at one side so 
that an armature two inches in diameter will rotate within 
them when made fast to the side-plates. The lugs are two 
inches and a half long, an inch wide, and two inches and a 
half high. 

Fromi iron five-eighths of an inch wide and one-eighth of 
an inch thick make two side-strips with L ends. These are 
four inches long, and are provided with two holes so that 
the machine-screws which hold the lugs to the inside plates 
will also hold these strips in place, at the outside, as shown 
in Fig. 45. At the rear these strips extend half an inch 
beyond the frame. Across the back a brass strip of the 
same size as the iron strips is arranged. It is held at the 
ends by screws, or small bolts, made fast to the L ends of 
the side-strips. Directly in the middle of the back- strip a 
hole is made for the armature shaft, and beyond it the pulley 
is ke^^ed or screwed fast to the shaft. 

At the front a similar strip is made and attached. This 
latter has a small hole in the middle of it to serve as a bear- 
ing for the forward end of the shaft. Across the top of the 

263 



ELECTRICITY BOOK FOR BOYS 

motor a brass strip or band is made fast with machine-screws ; 
and at the angles formed by the front ends of the side-strips 
and the front cross-strips hard- wood blocks are attached. 
To these the brushes and binding-posts are made fast, so 
that one brush at the top of the left-hand block rests on 




Tl&^/f 



the top of the commutator. The one at the underside of 
the opposite block must rest on the underside of the com- 
mutator. 

The armature core is made up of laminations as described 
for the dynamo armatures. In a really efficient motor the 
armature should have eight or more channels. 

The other parts of the motor may be assembled and 
wired as described on the preceding pages. The armature 
should be wound with No. 20 or 22 insulated copper wire, 

264 



DYNAMOS AND MOTORS 



and the field with No. i6 or i8. For high voltage, however, 
the armature should be wound with finer wire and a rheostat 
used to start it. 

A Third Type of Motor 

The third type is but a duplicate of the series-wound 
dynamo, the general plan of which is shown in Fig. 40. 

This motor can be made any size, but as its dimensions 
are increased the weight of the field -magnets and arma- 
ture must be proportionately enlarged. For an efficient 
and powerful motor, the field should stand ten inches high 
and six inches broad. The iron cores are five inches long 
and one inch and a half in diameter. These should be made 
by a blacksmith and bolted together. The armature is three 
inches in diameter and four inches long, and should develop 
two-thirds of a horse-power when sufficient current is run- 
ning through the coils to drive it at sixteen hundred revo- 
lutions. 

The wiring is carried out as shown in Fig. 40, and the 
armature hung and wound as suggested for the dynamo 
shown in Fig. 28, page 246. 



Chapter XI 

GALVANISM AND ELECTRO-PLATING 

Simple Electro-plating 

TO the average boy experimenter, electro-plating is one 
of the most fascinating of the uses to which electricity 
may be put. In scientific language the process is known as 
electrolysis, and involves the separation of a chemical com- 
pound into its constituent parts or elements by the action 
of an electric current and the proper apparatus. Elec- 
trolysis cannot take place, however, unless the liquid in 
the tank, commonly called the electrolyte (no relation to 
electric light), is a conductor. 

Water, or w^ater with mixtures of chemicals, such as sul- 
phate of copper, sulphate of zinc, chloride of nickel, cyanide 
and nitrate of silver, or uranium and other metallic salts, 
are good conductors. Oil is a non-conductor, and a current 
will not pass through it, no matter what the pressure may 
be. The simplest electro-plating outfit, and the one that 
a boy should start with, is the sulphate of copper bath, 
such as is commonly employed by makers of electrotypes, 
and which is in extensive use by refiners of copper for 
high-grade electrical use. 

More than half of the total output of copper in the world 

266 



GALVANISM AND ELECTRO-PLATING 

is used for electrical work — conductors, switches, and all 
sorts of parts — and since any impurity in the copper inter- 
feres with its conducting powers, it is most important that 
it should be free from any traces of carbon or arsenic. The 
electrol3rtic refining of copper is now a very important 
process in connection with electric work, and about half a 
million tons of copper are treated annually to free it from 
all impurities. Moreover, the gold, silver, and other valua- 
ble metals which may be found in copper-ore are thus 
recovered. 

The electro-plating, electrotyping, and refining operations 
are one and the same thing; but in the first instance the 
object to be plated is left in the solution only a short time 
or until a blush of copper has been applied. In the second 
process the wax mold is left in long enough for a thin 
shell of copper to be deposited; and in the third, the 
kathodes are immersed until they are heavily coated with 
copper. To carry on any of these operations it will be 
necessary to have a small tank or glass jar to hold the 
plating-bath or electrolyte. Preferably it should be of a 
square or oblong shape. But a serviceable tank may be 
constructed from white -wood, pine, or cypress, if proper 
care is taken in making and water-proofing (Fig. i). For 
experimental purposes a tank eighteen inches long, ten inches 
wide, and twelve inches deep will be quite large enough to 
use as a copper bath. For silver, nickel, or gold, smaller 
tanks should be employed, as they contain less liquid, or 
electrolyte, which in the more valuable metals is expensive. 

Obtain a clear plank twelve inches wide, well seasoned, 
and free from knots or sappy places. Cut two sides twenty 

267 



ELECTRICITY BOOK FOR BOYS 

inches long and two ends eight inches long. With chisel, 
saw, and plane shape the ends of the side planks as shown 
at Fig. 2 ; or if there is a mill at hand it would be well to 
have the ends cut with a buzz-saw, thus insuring that they 
will be accurate and fit snugly. Screw-holes are bored 
with a gimlet-bit, and countersunk, so that screws will pass 
freely through them and take hold in the edges of the 
boards. Screws and plenty of white -lead, or asphaltum 
varnish, should be used on these points to make them 
water-tight; then the lower edge of the frame is prepared 
for the bottom board. Turn the tank bottom up, and, 
with a fat steel- wire nail and a hammer, dent a groove at 
the middle of the edge of the planks all around, as shown 
in Fig. 3. It will not do to cut this out with a gouge- 
chisel, because it is intended that the wood should swell 
out again if necessary. The object of driving the wood 
down is to form a valley into which a line of cotton string- 
wicking, soaked in asphaltum varnish or imbedded in 
white-lead, may be laid. This should be done (as shown 
in Fig. 4) before the bottom is screwed on, so that after- 
wards (in the event of the joint leaking) the wood will 
swell and force the wicking out, and thus properly close 
the fissure. 

The bottom board should be provided with holes all 
around the edge, not more than two inches apart, through 
which screws can be driven into the lower edge of the 
tank. Treat the wood, both in and outside, to several 
successive coats of asphaltum varnish, and as a result you 
will have a tank resembling Fig. i. 

Two shallow grooves are to be cut in the top of each 

268 



GALVANISM AND ELECTRO-PLATING 

end board of the tank, for the cross-bars to fit in immova- 
bly. These bars should be about three inches apart; and 
the ones holding the anodes, or fiat copper plates, should 
be close to one side, leaving plenty of room for objects of 
various sizes to be properly immersed. 

Another m.anner in which the bottom of the tank can 
be attached is shown in Fig. 5, which is a view of the tank 
sides turned bottom up. A rabbet is cut from the lower 
edges of the sides and ends, before they are screwed to- 
gether, and a bottom is fashioned of such shape as to 
accurately fit in the lap formed by the rabbet. This rabbet 
and the outer edge of the bottom plank should be well 
smeared with white-lead, and all put together at the same 
time, driving the screws into the edge of the bottom plank, 
through the lower edges of the sides and bottom, and also 
through the bottom board into the lower edges of the sides 
and ends (Fig. 6). 

Still another and stronger way in which to make a tank 
for a large bath is to cut the planks as shown at Fig. 7. 
The sides are then bolted together, locking the ends and 
bottom, so that they cannot warp or get away. The bolts 
are of three-eighth-inch round iron-rod, threaded at both 
ends and provided with nuts. Large washers are placed 
against the wood and under the nuts, so that when the 
nuts are screwed on tightly they will not tear the wood, 
but will bear on the washers. The points are all to be 
well smeared with white-lead or acid-proof cement (see 
Formulae) before the parts are put together and bolted, so 
as to avoid any possibility of leakage. (Fig. 8 shows the 
completed tank.) 

269 




TANK FOR ELECTRO-PLATING 



GALVANISxM AND ELECTRO-PLATING 

Now obtain two c6pper rods long enough to span the tank, 
with an inch or two projecting beyond the tank at either 
side. At one end of these attach binding-posts, to which the 
wires from a battery can be connected, leaving the opposite 
ends free, as shown at Fig. 9 (see page 275). Anodes, or 
pure soft copper plates, are hung on the positive rod, while 
on the negative one the objects to be plated, or kathodes, 
are suspended on fine copper wires just heavy enough to 
properly conduct the current. The positive wire leads 
from the carbon, or copper pole, of the battery, while the 
negative one is connected with the zinc. The anodes are 
plates of soft sheet or cast copper, and should be as nearly 
pure as possible for electrol}d:ic work; but if they are to be 
re-deposited, to free them from impurities, they may be in 
thin ingot form, just as the copper comes from the mines. 

The general principle of electro-refining of copper is very 
simple. A cast plate of the crude copper is hung from the 
positive pole in a bath of sulphate of copper, made by dis- 
solving all the sulphate of copper, or bluestone, that the 
water will take up. Drop a few lumps on the bottom of 
the tank to supply any deficiency, then add an ounce of 
sulphuric acid to each gallon of liquid, to make it more 
active and a better conductor. 

The crude copper plate is to be the leading-in pole for 
the current, while a thin sheet of pure copper, no thicker 
than tissue-paper, is suspended from the opposite rod for 
the leading-out pole; or in place of the thin sheet, some 
coppei wires may be suspended from the rod. The elec- 
trodes — ^that is, the copper plate and the thin sheet or 
wires— are placed close together, so that the current may 

271 



ELECTRICITY BOOK FOR BOYS 

pass freely and not cause internal resistance in the battery. 
The electric current, in its passage from the crude copper 
plate to the pure copper sheet or wires, decomposes the 
sulphate of copper solution and causes it to deposit its 
metallic copper on the sheet or wires ; and at the same time 
it takes from the crude copper a like portion of metallic 
copper and converts it into chemical copper. The electric 
current really takes the copper from the solution and adds 
it to the pure copper sheet, while the remaining constituents 
of the decomposed solution help themselves to some copper 
from the crude plate. In this way the crude copper di- 
minishes and the pure copper sheet increases in size, the 
impurities as well as the salts of other metals being pre- 
cipitated to the bottom of the tank, or mingled with the 
solution, which must be purified or replaced from time to 
time by fresh solution. This is the process of copper- 
plating, and any metal object may be properly cleansed 
and coated with copper by suspending it in the bath and 
running the current through it. 

When the refining process is employed, any metal will 
answer as a depository for the copper, but as the intention 
is to produce a pure copper plate which can be melted and 
cast into ingots, it is of course necessary to have the original 
kathode of the same metal; otherwise an impure mixture 
will be the result. If, for example, a piece of cast-iron be 
used upon which to deposit the copper, then the iron will 
be enclosed in a deposit of pure copper; in other words, the 
result will be a heavily copper-plated piece of iron, and the 
smelting process will bring about a fusion of the two metals. 
It is not necessary to have absolutely pure copper for the 

272 



GALVANISM AND ELECTRO-PLATING 

anodes when copper-plating or electrotyping ; but the 
purer the copper the less the solution is fouled, and it will 
not require replenishing so often. 

An object intended to receive a plating of copper need 
not be of metal at all ; it may be of any material, so long as 
it possesses a conducting surface. A mold or a cast made 
of any plastic material, such as wax or cement, may have 
its surface made conductive by the application of graphite, 
finely pulverized carbon, or metal dusts held on by some 
medium not soluble in water. The wax molds, or im- 
pressions of type and cuts, are dusted with plumbago, and 
then suspended in the copper solution. A wire from the 
negative pole is connected so as to come in contact with 
the plumbago, and the copper deposit immediately begins 
to form on the face of the wax. When the film of copper 
has become heavy enough, the mold is drawn out of the 
solution, and the thin shell of metal removed from the wax 
and cut apart, so that each shell is separated from its 
neighbor and freed from marginal scraps. Flowers, leaves, 
laces, and various other objects can be given a coat of 
copper by thus preparing their surfaces, and some most 
beautiful effects may be secured by copper-coating roses; 
then placing them for a short time in a gold bath, and 
afterwards chemically treating the surface plating so as 
to imitate Roman, Tuscan, or ormolu gold, in bright or 
antique finish. Coins, medallions, bas-reliefs, medals, and 
various other things are reproduced by the electro-plating 
process, and their surfaces finished in gold, silver, bronze, 
or other effects. Years ago this was not possible, because 
the old method was to make a fac-simile cast in metal of 
i8 273 



ELECTRICITY BOOK FOR BOYS 

the object desired, and then chase or refinish the surface. 
This was a costly and tedious task. When BrugnalelH, an 
Itahan electrician, electro-gilded two silver coins in 1805, 
he laid the foundation for the modern process, but it did 
not come into general use until about 1839, when electro- 
plating and the electro-depositing of metals was begun on 
a practical scale. Before the invention of the dynamos 
for generating current, batteries had to be employed, and 
this made the process somewhat more expensive than the 
present method. Our boy amateurs, however, will have to 
be content with the battery system, since they are not sup- 
posed to have access to direct - current power, such as is 
used for arc or street lighting. 

Various forms of batteries may be used for this work, 
and they will be described in detail. For the copper-plat- 
ing bath it will be necessary to have the anodes of soft, 
cast, or sheet, copper sufficiently heavy so as not to waste 
away too quickly. These should be of the proper size to 
fit within the bath, and either one large one or several 
small ones may be employed. Stout copper bands should 
be riveted to the top of the plates, by means of which they 
miay be hung on the bar and so suspended in the solution 
(Fig. 10). The contact - points should be kept clean and 
bright, so that the current will not meet with any resistance 
in passing from the rod to the plates. 

In Fig. 9 a complete outfit is shown for any plating proc- 
ess, the difference being only in the solution and anodes. 
For silver-plating a silver solution and silver anodes are 
required, while for gold the gold solution and gold anodes 
will be necessary. In this illustration, A represents the 

274 



GALVANISM AND ELECTRO-PLATING 



tank, B the battery, C C the anodes, D D D the kathodes, or 
articles to be plated, E the positive rod, F the negative, 
and G, H the leading-in and leading-out wires. 

There is often a doubt in a boy's mind as to how the 
battery is to be connected up to the bath and the articles 
suspended in it. But there will be no difficulty about it 
once that the principle of the process is thoroughly under- 
stood. 

It is well to remember that the electro-plating bath is 
just the reverse of a battery in its action. The process 








carried on in a battery is the generation of electricity by 
the action of the acid on the positive metal, accompanied 
by the formation of a salt on one of the elements ; while in 
the plating-bath the current from an external source (the 
battery or dynamo) breaks up the salts in solution and 
deposits the metal on one of the elements (the kathode). 

The remaining element in the solution attacks the salts, 
in chemical lumps or granular form, and dissolves them to 
take the place of the exhausted salts; or it attacks the 

275 



ELECTRICITY BOOK FOR BOYS 

metal anode from which these salts were originally made, 
and eats off the portion necessary to replace the loss caused 
by the action of the current in depositing the fruits of this 
robbery in metallic form upon the article to be plated (the 
kathode). There should be no confusion in the matter of 
properly connecting the poles if one remembers that the 
current is flowing through the battery as well as through 
the wires and the solution in the tank. 

Get clearly in your mind that the current originates in 
the battery of zinc and carbon or zinc and copper. The 
zinc is electro-positive to carbon or copper, and at a higher 
electric level the current flows from the zinc plate inside 
the cell to the carbon or copper; therefore, the zinc is the 
positive pole. Now the current, having flowed through the 
battery from zinc to carbon, or the negative plate, is bound 
to flow out of the battery from the carbon through the 
apparatus and back again to the zinc in the battery. There- 
fore, the wire (G) attached to the carbon of the battery 
leads a positive or + current, although the carbon is 
negative; in the battery, and the wire (H) leading out is 
negative, or — , although it returns the current to the 
positive pole of the battery. 

This is the simple explanation of the circulation of cur- 
rent; but to cut it down still more, always remember to 
attach the wire from the anode rod to the carbon, or copper, 
of the battery, and the kathode rod to the zinc of the 
battery. 

In copper-plating this is easy to determine without any 
regard to wires, because if the wires are misconnected there 
will be no deposit, and the kathode will turn a dark color. 

276 



GALVANISM AND ELECTRO-PLATING 

If everything is all right a slight rose-colored blush of 
copper will appear at once on the kathode. Too little 
current will make the process a long and tedious one, while 
too much current will deposit a brown mud on the kathode, 
which will have to be washed off or removed and the article 
thoroughly cleansed before a new action is allowed to take 
place. 

With a series of cells it is an easy matter to properly govern 
the current by cutting out some of the cells or by using 
resistance-coils (see chapter vii. on Electrical Resistance). 

Cells and batteries for electro-plating may be made or 
purchased, and primary batteries should be used. The use 
of the secondary or storage-battery is not necessary for 
plating purposes, since no great volume of current is needed, 
and it can be generated' in a battery of cells while the work 
is going on. 

One of the best primary batteries is the Benson cell, 
shown in connection with the plating-bath, and also in Fig. 
II. It consists of an outer glass jar (G J), which contains 
a cylinder of amalgamated zinc (Z-h, or positive) covered 
with diluted sulphuric acid — one part acid to three parts 
water. An inner porous cup (P C) contains concentrated 
nitric acid, into which the carbon (C — , or negative) is 
plunged. The liquid in the inner cup and glass cell should 
be at the same level. 

There is no polarizing in this cell, for the hydrogen 
liberated at the zinc plate, in passing through the nitric 
acid on its way to the carbon-pole, decomposes the nitric 
acid and is itself oxidized. A cell with a glass jar six inches 
in diameter and eight inches high will develop about two 

277 




J\Qr\ 



THE BENSON CELL PRIMARY BATTERY 
278 



GALVANISM AND ELECTRO-PLATING 

volts of electro-motive force; and as its internal resistance 
is very low it will furnish a steady current for several hours. 
Any number of these cells may be made and connected in 
series; but when not in use it would be well to remove and 
wash the zincs. Any bichromate battery will answer very 
well for plating, the Grenet being an especially good one. 
A well-amalgamated zinc plate forms one pole, and a pair 
of carbon plates, one on each side of the zinc and joined at 
the top, make up the other pole. When not in use the 
entire plunge part should be removed from the bichromate 
solution, rinsed off in water, and laid across the top of the 
jar, ready for its next employment. The zinc and carbons 
must be joined together so that they are well insulated, and 
with no chance of the zinc coming into contact with the 
carbons. This may be done with four pieces of hard- wood 
soaked in hot paraffine and then locked together with 
stove-bolts and nuts, as shown at Fig. 12. Holes must be 
made in the top corners of the carbons and zinc, and with 
small bolts and nuts the connecting wires can be made 
fast. 

To charge this battery, add five fluid ounces of sulphuric 
acid to three pints of cold water, pouring the acid slowly 
into the water and stirring it at the same time with a glass 
or carbon rod. When this becomes cold, after standing a 
few hours, add six ounces of finely pulverized bichromate 
of potash. Mix this thoroughly, and pour some of the 
solution into the glass cell until it is three-fourths full ; 
then it will be ready to receive the carbons and zinc. When 
arranging the wood-clamps on the carbon and zinc plates 
it would be well to make two of the clamps longer than the 

279 



ELECTRICITY BOOK FOR BOYS 



others so that they will extend out far enough to rest on 
the top edge of the jar. To keep them in position at the 
middle of the jar, notches should be cut at the underside 
of these clamps, so that they will fit down over the edge of 
the jar. Any number of these cells may be connected to- 
gether to obtain the desired amount of current, or electro- 
motive force. 

Other batteries suitable for electro-plating are the Edison 
primary, Taylor, Fuller, Daniell, gravity, Groves, and 
Merdingers. All of these may be purchased at large elec- 
trical equipment or supply houses. 

The Cleansing Process 

One of the most important operations of the plating 
process is to properly cleanse the articles to be plated 
before they are placed in the bath. When once cleaned 
the surfaces of these objects must not be touched with the 
fingers, or any dusty or greasy object ; otherwise the electro- 
deposited metal will not hold on the surface, but will peel 
off, in time, or blister. A very small trace of foreign 
matter is sufficient to prevent the deposit from adhering 
to the surface to be plated; therefore, great care must be 
taken to eliminate all trace of an3rthing that would inter- 
fere with the perfect transmission of metallic molecules to 
the prepared surfaces. Acids are chiefly employed to re- 
move foreign matter from new metallic surfaces; and for 
copper, brass, iron, zinc, gold, and silver a table is given on 
page 281 which will show the right proportion of acids to 
water in order to cleanse the various metals. In the follow- 

280 



GALVANISM AND ELECTRO-PLATING 

ing scale the numerals stand for parts. For example : the 
first one means loo parts water, 50 parts nitric acid, 100 
parts sulphuric acid, and 2 parts hydrochloric acid — making 
in all 252 parts. These can be measured in a glass graduate. 





Water 


Nitric 
Acid 


Sulphuric 
Acid 


Hydrochloric 
' 'Acid 


Copper and brass 


100 
100 
100 
100 
100 
100 


50 

10 
2 
3 


100 

*"8 
12 
10 


2 
15 


Silver 


Wrought-iron 


2 


Cast-iron 


3 


Zinc. . ... 







Twist a piece of fine copper wire about part of the object 
to be cleaned and plated; then dip it in the acid and rinse 
off in clean warm or hot water, and rub the surface briskly 
with a brush dipped in the liquid. Dip it again several 
times, and rinse in the same manner ; then, when it is bright 
and clean, place it in the bath, twist the loose end of the 
wire around the negative rod, and start the current flowing, 
taking care that the object is thoroughly immersed. 

Tarnished gold or silver articles may be cleaned by im- 
mersing them in a hot solution of cyanide of potassium; 
or a strong warm solution of carbonate of ammonia will 
loosen the tarnish on silver, so that it can be brushed off. 
Corroded brass, copper, German-silver, and bronze should 
be cleansed in a solution composed of sulphuric acid, three 
ounces ; nitric acid, one and three-quarters ounces ; and 
water, four ounces. This soon loosens and dissolves the 
corrosion; then the article should be brushed off, dipped in 
hot water, and rinsed. Then replace it in the solution for 

281 



ELECTRICITY BOOK FOR BOYS 

a minute or two and rinse again, when it will be ready for 
the plating-bath. 

Corroded zinc should be immersed in a solution of sul- 
phuric acid, one ounce; hydrochloric acid, two ounces; and 
distilled or rain water, one gallon. It should be well brushed 
after the acid has bitten off the corrosion. 

Rusty iron or steel should be pickled in a solution of 
sulphuric acid, six ounces, hydrochloric acid, one ounce, 
and water, one gallon. When the rust has been removed, 
immerse the object in a solution composed of sulphuric acid, 
one pint, and distilled water, one gallon. Before the acid 
is added to the water dissolve one-quarter-pound of sul- 
phate of zinc in the water; then add the acid, pouring it 
slowly and stirring the water. 

Lead, tin, pewter, and their compounds may be cleansed 
by immersing them in a hot solution of caustic soda or 
potash, then rinsing in hot water. Take great care if 
caustic is used, as it will burn the skin and tissues of 
the body. Do not let the fingers come into contact with 
any cleansed article, because the oily secretions of the body 
will stick to the m.etal and cause the coat of deposited metal 
to strip off or present a spotted appearance. 

The Plating-bath 

The object to be plated should not touch the bottom or 
sides of the plating-vat, and it should be far enough away 
from the anodes to avoid any possibility of coming into 
contact with them. It will not do to place the anode and 
kathode too close together, as the plate will be deposited 

282 



GALVANISM AND ELECTRO-PLATING 

unevenly; the thicker coating will appear on the parts 
closest to the anode. Neither should they be separated too 
far, as the resistance of the cell is thereby increased, and of 
course this means a waste of energy. The knowledge of how 
to arrange the anode and kathode is a matter to be learned 
by experience, but by carefully watching the deposit it will 
not be a difficult matter to determine the proper positions. 

For many reasons the glass tank is preferable for ama- 
teur electro-plating work, since the objects may be watched 
without disturbing their electric connections and without 
removing them from the liquid. A very good plan for the 
copper bath, when spherical, cylindrical, or hollow objects 
are to be plated, is to line the inside of the tank with strips 
or a sheet of copper, hung on hooks that will catch on the 
sides ; then connect the positive wire directly to these strips. 
With this arrangement but one rod, the negative, is in use, 
and the objects to be plated are suspended from it. It 
follows that the objects will take up the copper deposit 
from all sides, and a more evenly distributed coating will 
be the result. 

It is better to start up the current gradually, rather than 
to put on at the beginning a large amount of electro-motive 
force. By watching the character of the deposit you can 
soon tell if you have the proper strength of current. If 
everything is working properly the copper deposit will have 
a beautiful flesh tint; but if the current is too strong it 
takes on a dark-red tone and resembles the surface of a 
brick. This is not right, and the object must be removed 
and washed off, the current reduced, and the object re- 
placed in the bath. 

283 



ELECTRICITY BOOK FOR BOYS 

When a sufficiently heavy coating of the copper has been 
appHed, remove the object and wash thoroughly in running 
or warm water to free it from any remaining copper fluid. 
If this is not done the surface, in drying, will turn a dull 
brown, and will have to be bitten off with the acid solution 
for cleansing copper. 

The finer the copper deposit the better and smoother it 
will be; the grain will be smaller, and it will not present a 
rough surface, which is always difficult to plate over with 
silver or gold, unless a frosted effect is desired. Non-con- 
ducting objects are usually plated with copper first, and 
then replated with the metal desired for the final finish. 

To make the surface conductive, finely powdered black- 
lead, or plumbago of the best kind, or finely pulverized 
gas-carbon is brushed over the surface. This must be thor- 
oughly done; and if the deposit is slow about appearing at 
any spot it may be hastened by touching it with the end of 
an insulated wire attached to the main conductor. This, 
of course, will only answer for objects strong enough to 
stand the brushing treatment; it will not do for flowers, 
insects, and other delicate things, that are to be silver or 
gold plated. These should be given a film of silver by soak- 
ing in a solution of alcohol and nitrate of silver, made by 
shaking two parts of the chemical into one hundred parts 
of grain-alcohol, with the aid of heat and in a well-corked 
bottle. When dry, the object should be subjected to a 
bath of sulphuretted hydrogen gas under a hood. The 
sulphuretted hydrogen is made by bringing a bar of wrought- 
iron to a white-heat in the kitchen range or furnace fire, and 
touching it with a stick of sulphur. The iron will melt and 

284 



GALVANISM AND ELECTRO-PLATING 

drop like wax. These drops should be collected in a bottle. 
Now pour over them diluted sulphuric acid, one part acid to 
three parts water, and the gas will at once rise. It will be 
quickly recognized by its odor, which is similar to that of 
over-ripe eggs. It can be led off through a tube to the 
place where you wish to use it, and when through, the 
operation of gas-generation may be stopped by pouring off 
the liquid. 

All objects prepared in this way should be given a pre- 
liminary coating of thin copper before they are plated with 
any other metal. 

Silver-plating 

Plating in silver is done in practically the same way as 
described for the coppering process. Thin strips or sheets 
of pure silver are used for the anodes, and the electrolyte 
is composed of nitrate of silver, cyanide of potassium, and 
water. 

Dissolve three and one-half ounces of nitrate of silver in 
one gallon of water; or if more water is needed to fill the 
tank, add it in the proportion of three and one-half ounces 
of the nitrate to each gallon of water. Dissolve two ounces 
of cyanide of potassium in a quart of water, and slowly add 
this to the nitrate solution. A precipitate of cyanide of 
silver will be formed. Keep adding and stirring until no 
more precipitate is formed, but be careful not to get an 
excess of the cyanide in the solution. 

Gather this precipitate, and wash it on filtering-paper by 
pouring water over it. The filter-paper should be rolled in 
a funnel shape thus permitting the water to run aw^ay 

285 



ELECTRICITY BOOK FOR BOYS 

and leaving the precipitate in the paper. This precipitate 
is to be dissolved in more cyanide solution, and added to 
the quantity in the tank. There should be about two 
ounces of the potassium cyanide per gallon over and above 
what was originally put in. 

The silver anodes show the condition of the fluid. If 
the solution is in good order they will have a clear, creamy 
appearance, but will tarnish or turn pink if there is not 
sufficient free cyanide in the solution. 

The proper strength of current is indicated by the ap- 
pearance of the plated objects. A clear white surface 
shows that everything is all right, the solution in proper 
working order, and the proper current to do the work. 
Too much current will make the color of the kathodes 
yellow or gray, while too little current will act slowly and 
require a long time to deposit the silver. 

The adhesion of silver-plate is rendered more perfect by 
amalgamating the objects in a solution of nitrate of mercury, 
one ounce to one gallon of water. After the objects have 
been properly cleansed they are immersed in this solution 
for a minute, then placed in the silver-bath and connected 
with the negative-rod, so that the electro-depositing action 
begins at once. 

Gold-plating 

The gold-bath is made in the same manner as the silver 
one just described, with the exception that chloride of gold 
is used in place of the nitrate of silver in the first solution. 
This solution must be heated to 150° Fahrenheit when the 
process is going on ; or a cold bath may be made of water, 

286 



GALVANISM AND ELECTRO-PLATING 

5000 parts; potassium cyanide, one hundred parts; and pure 
gold, fifty parts. The gold must be dissolved in hydro- 
chloric acid, and added to the water and potassium. 

Very pretty effects may be obtained in gold-plating by 
changing the tones from yellow to a greenish hue by the 
addition of a little cyanide of silver to the solution, or by 
the use of a silver anode. A reddish tinge may be had 
by adding a small portion of sulphate of copper to the 
solution, or hanging a small copper anode beside the gold 
one. In the hot gold-bath the articles should be kept in 
motion, or the solution stirred about them with a glass 
rod. 

When the solution is perfectly balanced and working 
right the anodes should be a clear dead yellow, and the 
articles in process of plating should be of the same hue. 

A gold-plating outfit is shown in Fig. 13, and consists of 
the tank and bath, a cell, and a resistance-coil (R), through 
which the strength of the current is regulated. 

The current, passing out of the cell from the carbon (C), 
is regulated through the resistance-coils (R) by the switch 
(S). From thence it passes to the rod from which the 
anode (A) is suspended, across the electrolyte (E) to the 
kathode (K), on which the metal is deposited, and then 
returns through the negative wire to the zinc (Z) in the 
cell. If the hot bath is used the gold solution may be con- 
tained in a glazed earthen jar or a porcelain-lined metal 
jar or kettle. But if the latter is used care must be taken 
to see that none of the enamel is chipped, or a short-circuit 
will be established between the rods. This jar or kettle 
may then be placed on a gas-stove, and a thermometer 

287 



ELECTRICITY BOOK FOR BOYS 

should be suspended so that the mercury bulb is half an 
inch below the surface of the liquid, as shown at T in Fig. 
13. As the liquid simmers or evaporates away a little 




water should be added from time to time to keep the bulk 
of the liquid up to its normal or original quantity. 



Nickel-plating 

The nickel-plating process is similar, in a general way, 
to the others ; it is carried on in a cold bath — ^that is, at the 
normal temperature, without being heated or chilled arti- 
ficially. 

288 



GALVANISM AND ELECTRO-PLATING 

There are a great many formula for the nickel as well 
as for the other baths, but the generally accepted one is 
composed of double nickel ammonium-sulphate, three parts ; 
ammonium carbonate, three parts ; and water, one hundred 
parts. Another good one is composed of nickel sulphate, 
nitrate, or chloride, one part ; sodium bisulphate, one part ; 
and water, twenty parts. 

Nickel anodes are used in bath to maintain the strength, 
and great care must be taken to have the bath perfectly 
balanced — that is, not too acid nor too alkaline. 

To test this, have some blue-and-red litmus paper. If 
the blue paper is dipped in an acid solution, it will turn red; 
and back to blue again if placed in an alkaline solution. 
If the nickel solution is too strong with alkali, a trifle more 
of the nickel salts must be added, so that both the red-and- 
blue litmus paper, when dipped in the liquid, will not 
change color. If the bath is too alkaline, it will give a dis- 
agreeable yellowish color to the deposit of metal on the 
kathode ; and if too acid, the metal will not adhere properly 
to the kathode, and will strip, peel, or blister off. 

Finishing 

When the articles have been plated they will have a 
somewhat different appearance to what may have been 
expected. For instance, copper-plated articles will have a 
bright fleshy-pink hue ; silver, an opaque creamy - white ; 
gold, a dead lemon-yellow color, and nickel much the ap- 
pearance of the silver, but slightly bluer in its tone. Articles 
removed from the bath should be shaken over the bath so 
19 289 



ELECTRICITY BOOK FOR BOYS 

as to remove the solution ; then they should be immediately 
plunged into hot water, rinsed thoroughly, and allowed to 
dry slowly. 

When a silvered or gilded object is perfectly dry it should 
be rubbed rapidly with a brush and some fine silver-polish- 
ing powder until the opaque white or yellow gives place to 
a silver or gold lustre. It will then be ready for burnishing 
with a steel burnisher, or the article may be left with a 
frosted silver or gold surface. Steel burnishers can be had 
at any tool-supply house, and when used they should be 
frequently dipped in castile soapy water to lubricate them. 
They will then glide smoothly over the surface of the deposit- 
ed metal, driving the grain down and making it bright at the 
same time. If the soapy water were not used the action of 
the hard burnisher over the plate would have a tendency 
to tear away the film of deposited metal. The burnisher 
must always be clean and bright, otherwise it would scratch 
the plated articles; and, when not in use, keep the bright 
polishing surfaces wrapped in a piece of oiled flannel. 

Small articles, such as sleeve-buttons, rings, studs, and 
other things not larger than a twenty-five-cent piece, may 
be polished by being tumbled in a sawdust bag. A cotton 
bag is made, three feet long and six inches in diameter, 
closed at one end and half -filled with fine sawdust. The 
articles are then put in the bag and the end closed. Grasp 
the ends of the bag with both hands, as if to jump rope with 
It; then swing it to and fro, until the articles have had a 
good tumbling. Look at them to see if they are bright 
enough; if not, keep up the tumbling. 

When old work is to be re-plated, or gone over, it will be 

290 



GALVANISM AND ELECTRO-PLATING 

necessary to remove all of the old plate before a really good 
job can be done. In some cases it may be removed with a 
scratch-brush or pumice-stone; but, as a rule, it can be 
removed much quicker and more satisfactorily with acids. 
Silver may be removed from copper, brass, or German- 
silver with a solution of sulphuric acid, with one ounce of 
nitrate of potash to each two quarts of acid. Stir the 
potash into the acid, then immerse the article. If the 
action becomes weak before the silver is all off, then heat 
the solution and add more of the potash (saltpetre). Gold 
may be removed from silver by heating the article to a 
cherry-red, and dropping it into diluted sulphuric acid — 
one part acid to two parts water. This will cause the gold 
to peel and fall off easily. 

Electrotyping 

The term electrotyping is interpreted in several ways, 
but, in general, it means the process of electro-plating an 
article, or mold, with a metal coating, generally copper, of 
sufficient thickness, so that when it is removed, or sepa- 
rated from its original, it forms an independent object 
which, to all appearances, will be a fac-simile of the original. 

To obtain a positive copy a cast has to be taken from a 
negative or reverse. This negative is called the mold or 
matrix, and can be of plaster, glue, wax, or other composi- 
tions. There are a number of processes in use, but the 
Adams process (no relation to the author) will give a boy a 
clear idea of this electro-chemical and mechanical art. 
This process was patented in 1870, and is said to give a 

291 



ELECTRICITY BOOK FOR BOYS 

perfect conduction to wax and other molds, with greater 
certainty and rapidity than any other, and will accomplish 
in a few minutes that which plumbago (black-lead) alone 
would require from two to four hours to effect. 

As applied to the electrotyping of type, and cuts for 
illustration, the warm wax impression is taken by pressing 
the chase or form of type into a bed of wax by power or 
hydraulic pressure. Then remove it, and while the wax is 
still warm, powdered tin, bronze, or white bronze powder 
is freely dusted all over it with a soft hair-brush, until the 
surface presents a bright, metallic appearance. The super- 
fluous powder is then dusted off, and the mold is immersed 
in alcohol, and afterwards washed in water to remove the 
air from the surface. It is then placed in the copper bath 
and the connection made from the negative pole to the face 
of the mold, so that the current will flow over its entire 
surface. A' deposit of copper will quickly appear, and be- 
come heavier as the mold is left in longer. 

When a mold has received the required deposit it should 
be taken from the bath and the copper film removed from 
it. This is done by placing the mold in an inclined posi- 
tion and passing a stream of hot water over the back of the 
copper film. This softens the wax and enables one to strip 
the film off, taking care at the same time not to crack or. 
bend the thin copper positive. 

The thin coating of wax, which adheres to the face of the 
copper, can be removed by placing it, face up, on a wire 
rack and pouring a solution of caustic potash over it, which, 
in draining through, will fall into a vessel or tank beneath 
the rack. 

292 



GALVANISM AND ELECTRO-PLATING 

The potash dissolves the wax in a short time, and the 
electro-deposited shell may then be rinsed in several changes 
of cold water, or held under the faucet until thoroughly 
freed from the caustic. 

As many, if not all, of the chemicals used in the various 
plating processes, and also the cleaning fluids, are highly 
poisonous, great care should be taken when handling them. 
Do not let the fingers or hands come in contact with 
caustic solutions or cyanide baths. 

Never use any of these solutions if you have recently cut 
your fingers or hands, and do not allow the cyanides or 
caustics to get under the finger-nails. Never add any acid 
to liquids containing cyanide or ferro - cyanide while in a 
closed room. This should always be done in the open air, 
where the fumes can pass away, for the gases which rise 
from these admixtures are poisonous when inhaled. 



Chapter XII 

MISCELLANEOUS APPARATUS 

THE field of applied electricity is such a wide one as 
to preclude any exhaustive handling of the subject in 
a book of this size. The aim has been to acquaint the 
young student with the basic principles of the science, and 
it is his part to develop these principles along the lines in- 
dicated, in the preceding pages. But there are some prac- 
tical applications that may be properly grouped under the 
heading of this chapter. They may serve as a stimulus to 
the inventive faculties of the youthful experimenter, and 
since the pieces of apparatus now to be described are use- 
ful in themselves, the time spent in their construction will 
not be wasted. 

A Rotary Glass-ctittcr 

When making a circle of glass it is generally best to let 
a glazier cut the disk, otherwise many panes are likely to 
get broken before the young workman succeeds in getting 
out a perfect one. But with a rotary glass-cutter the task 
is a comparatively simple one, and the tool is really an 
indispensable piece of apparatus in every electrician's kit. 
(See Figs, i and 2.) 

294 



MISCELLANEOUS APPARATUS 

The wooden form is turned from pine or white- wood, and 
is three inches in diameter at the large end, or bottom, one 
inch in diameter at the top, and two inches high. It is 
covered with felt held on with glue. Directly in the mid- 
dle of the top a small hole is bored one-eighth of an inch 
in diameter, and in this aperture an awl or marker is placed, 
handle up, as shown in Fig. 2. Notice that the awl is not 
made fast to the form, but is removable at pleasure. A 
hard brass strip twelve inches long, five-eighths of an inch 
wide, and one-eighth of an inch thick is cut at the end to 
receive a steel-wheel glass-cutter, as shown at the foot of 
Fig. I. 

A number of one-eighth-inch holes are bored along the 
strip, and half an inch apart, measuring from centre to 
centre. To cut a disk of glass the form is placed at the 
centre of the pane, the latter being imposed on a smooth 
table-top over a piece of cloth. The strip, or arm, is laid 
on the form, and over a small washer, so that one of the 
holes lines with that in the form. The awl is passed down 
through the strip and into the block, and the cutter is ar- 
ranged in the slot at the end of the arm. Press down light- 
ly on the handle of the awl, to keep the form from slipping; 
then the cutter is drawn around the glass, describing the 
circle, and cutting the surface of the glass, as shown by the 
solid line in Fig. 4. The disk must not be removed from 
the pane until the margin is broken away. With a straight- 
edge and a cutter score the glass across the corners, as in- 
dicated by the dotted lines in Fig. 4 ; then tap the glass at 
the underside along the line and break off the corners. 
After the corners have been removed tap the glass again, 

295 




riGr.6. 



riGr/f. 



GLASS-CUTTING APPLIANCES 
296 



MISCELLANEOUS APPARATUS 

following the line of the circle; then break away the re- 
maining fragments and smooth the edge. 

To Smooth Glass Edges 

To smooth the rough edge of glass there are several 
methods. The simplest way is to hold the disk or straight- 
edge against a fine grindstone and use plenty of water. 
The glass must be held edgewise, as shown in Fig. 5, and 
not fiatwdse, as shown in Fig. 6. To properly grind a disk 
two workmen are necessary, one to turn the stone, and 
the other to hold the disk by spreading the hands and 
grasping it at the middle on both sides (see Fig. 5). In 
this manner the glass may be held securely, and slowly 
turned, so that an even surface will be ground. When the 
flat edge is smoothed, tilt the glass first to one side and 
then the other, and grind off the sharp edges. 

Another method is to lay the glass on a table, upon a 
piece of felt or cloth, and allow the edge to project over 
the table for two or three inches. Hold the glass down 
with one hand to prevent its slipping; then, with a piece 
of corundum, or a rough whetstone and glycerine, work 
down the edge until it is smooth, turning the glass con- 
tinually so that the edge you are w^orking on hangs over 
the table. This process of grinding is somew^hat tedious, 
but perseverance and patience will win out. 

To Cut Holes in Glass 

Holes may be cut in glass in several ways by an expert, 
but the boy who is a novice in this line should stick to 

297 



ELECTRICITY BOOK FOR BOYS 

slow and sure methods and take no chances. Fortunately, 
glass is little used in voltaic electricity, but it is indispen- 
sable in the construction of the f rictional machines, Ley den- 
jars, and condensers, where glass is used as the dielectric, 
also for the covering-plates to instruments. 

The simplest method is that of rotating a copper tube 
forward and backward over the glass, using fine emery 
dust for the cutting medium and oil of turpentine as a 
lubricant. The copper tube must be held in a rack, so 
that its location will not shift during the rotating or cut- 
ting motion. The rack in which the tube is held may be 
of any size, but to take a disk or square of glass, twenty 
inches across, the frame should be twenty-two inches long, 
ten inches wide, and twelve inches high, as shown in Fig. 3. 

The side -plates are eleven inches high and ten inches 
wide, the top is twenty-two inches long and ten inches 
wide, while the under ledge is twenty and a quarter inches 
long by ten inches wide. This frame is put together with 
glue and screws. Across the back, from the corners down 
to the middle of the under ledge, battens or braces are 
made fast to prevent the frame from racking. A hole is 
made through the middle of the top and under ledge for 
the copper tube to pass through. If different-sized tubes 
are to be used, blocks to fit the top and under board are 
to be cut and bored, so that they may be held in place 
with screws when in use. To cut a hole in glass, place the 
disk or pane on a felt or cloth-covered table, and over it 
arrange the frame, so that the tube will rest on the spot to 
be drilled. Drop the copper tube down through the hole, 
having first spread the bottom of the tube slightly, so that 

298 



MISCELLANEOUS APPARATUS 

it will not split the glass. Now put some emery inside the 
tube so that it will fall on the glass; then place a wooden 
plug in the top of the tube and arrange an awl, or hand- 
plate, so that the tube may be pressed down. Take one 
turn about the tube with a linen line, or gut-thong, and 
make the ends fast to a bow, so that it will draw the string 
taut but not too tight. Lubricate the foot of the tube 
with oil of turpentine, and. draw the bow back and forth. 
At first the motion will cause the copper to scratch the 
glass, and then cut it, until finally a perfectly drilled hole is 
formed. During the operation both glass and frame must 
be held securely, and the bow drawn evenly and without 
any jerking motion. Holes of different sizes may be cut 
with tubes of various diameters. Small holes may be cut 
with a highly tempered steel-drill and glycerine, the drill 
being held in a hand-drilling tool or in a brace. 

Anti-hum Device for Metallic Lines 

• In overhead wires, where galvanized or hard copper wire 
is used, the hum due to the tension of the wires, and the 
wind blowing through them, causes a musical vibration 
which becomes most annoying at times. This can be over- 
come by a simple device known as an "anti-hum." It con- 
sists of a knob made of wood or rubber, through which a 
hole is bored, and around which a groove is cut. One end 
of the wire is passed through the hole and a loop formed, 
the loose end being wrapped about the incoming wire. 
The other end of the line is passed around the knob in the 
groove, and the end twisted about the line-wire. The knob 

299 



ELECTRICITY BOOK FOR BOYS 



is then an insulator and a sound-deadener at the same time. 
To complete the metallic circuit a loop of wire is passed 
under the knob, the ends of which are made fast to the 
line-wires, as shown at Fig. 7. 



A Reel-car for Wire 

It is not always convenient nor possible to carry about 
a heavy roll of wire when hanging a line, especially if it is 
No. 12 galvanized wire, of which there are from fifty to a 
hundred pounds in one roll. Wire should be unwound as 




it is paid out, and not slipped off from the coil, since it is 
liable to kink ; therefore, some portable means of transport- 
ing it should be provided. Line-wires over long distances 
are paid out from a reel-truck drawn by horses. For the 

300 



MISCELLANEOUS APPARATUS 

use of the amateur electrician the reel-car shown in Fig. 8 
should meet all requirements. 

The reel is made from two six-inch boards, a barrel- 
head or a round platform of boards, four trunk-rollers, and 
a bolt. From a six-inch board cut two pieces five feet 
long. Eighteen inches from either end cut one edge away 
so as to form handles, as shown at C C C C in Fig. 8, round- 
ing the upper and under edges to take off the sharp cor- 
ners. Cut four cross-pieces sixteen inches long; and from 
two-by-four-inch spruce joist cut four legs twelve inches 
long, and plane the four sides. 

Nail two of the cross-pieces to the legs; then nail on the 
side-boards and so form the frame of the reel. Bore a half- 
inch hole through a piece of joist; then nail it between the 
remaining two cross-boards, taking care to get it in the 
centre, as show^n at A. Arrange these pieces at the mid- 
dle of the frame, making them fast with nails driven through 
the side-boards and into the ends of these cross-pieces. 
Drive some pieces of matched boards together, and with 
a string, a nail, and a pencil describe a circle twenty inches 
in diameter. With a compass-saw cut the boards on the 
line, and join them with four battens made fast at the under- 
side with nails. Do not make the battens so that they will 
extend out to the edge of the circle, but keep them in an 
inch or two, so that the under edge of the turn-table will 
rest on four trunk-rollers screwed fast to the top edges of 
the side-boards and end cross-pieces, as shown at B. A 
half -inch bolt is passed down through a hole made at the 
middle of the table, and through the, block. Between the 
block and the underside of the table several large iron 

301 



ELECTRICITY BOOK FOR BOYS 

washers should be placed on the bolt, so that they will keep 
the table slightly above the rollers, the main weight of the 
table and its load of wire being held by the middle cross- 
brace. The object of the trunk - rollers is to relieve the 
side strain on the bolt, and also to prevent friction between 
the edge of the table and the frame, in case the tension on 
the wire pulls it to one side. Bore six holes in the table, 
on a circle of twelve inches, and drive hard-wood pegs in 
them, as shown in Fig. 8. When a roll of wire is lying on 
the table two boys can easily lift and carry the car, and as 
they do so the wire will pay out. Give all the wood- work 
a coat of dark -green paint, and oil the trunk -rollers and 
the wood where the bolt passes through. A pair of nuts 
should be placed on the lower end of the bolt and a washer 
under its head. These lock-nuts must be screwed on with 
two monkey-wrenches, forced in opposite directions, so that 
one nut will be driven tightly against the other. This is to 
prevent the turning of the table from unscrewing the nuts. 

Insulators 

For telegraph and telephone lines, where pole, tree, or 
building attachments are necessary, insulators must be used 
to carry the wires without loss of current. The regular 
glass, porcelain, or hard rubber insulators, made for pole 
and bracket use, are of course the best. They can be pur- 
chased at any supply-house for a few cents each, but there 
are other devices which will answer equally well and which 
will cost little or nothing. 

Obtain some bottles of stout glass, the green or dark 

302 



MISCELLANEOUS APPARATUS 

glass being the toughest; then carefully break the bottle 
part away. In doing this hold the bottle by the neck, 
with a piece of old cloth wrapped about it, to prevent the 
glass chips from flying. Save all of the neck and part of 
the shoulder, as shown in Fig. 9, so that the wire and its 
anchoring loop will not slip off and fall down on the peg 
or cross-tree. 

Hard -wood pegs cut from sticks one inch and a half 
square should be whittled down so that they will fit in the 
neck and come up to the top. The pegs should be long 
enough at the bottom to permit of their being fastened to 
the supporting poles, trees, or building. In Fig. 10 three 
ways of attaching insulators are shown. At A the peg is 
nailed to the top of a pole, or a hole is bored in the pole 
and the peg driven down in it. At B two sticks with peg 
ends are nailed to a pole in the form of a V, and across 
the sticks a cross-brace is made fast to prevent the sticks 
from spreading or dropping down. This cross -brace is 
made fast to both the sticks and the pole so as to form 
a rigid triangle. At C the usual form of cross-tree, or J 
brace, is shown. The pegs may be nailed to the face of the 
cross-plate, or holes may be bored in the top and the pegs 
driven down into them. If the cross-piece is more than 
two feet long, bracket-iron should be screwed fast to the 
pole and brace at both sides, as shown at C. Where a cross- 
plate is made fast to a pole, a lap should be cut out so that 
the plate can lie against a flat surface rather than on a 
round one (see D in Fig. 10). 

The shoulder of the bottle-necks must not rest on a cross- 
piece, or touch anything that would lead to the ground or 

303 



ELECTRICITY BOOK FOR BOYS 

to other wires. The shoulder acts as a collar, and so sheds 
water that in wet weather the current cannot be grounded 
through the rain. The underside of the collar should al- 
ways be dry, and also that part of the peg protected by the 
collar, thereby insuring against the loss of current. The 
relative position of insulator and peg is shown at Fig. 9, 
and if the pegs are cut carefully the bottle-necks should 
fit them accurately. 

Joints and Splices 

It is essential in electrical work to have joints, splices, 
unions, and contacts made perfectly tight, so that the cur- 
rent will flow through them uninterruptedly. A poor contact 
or weak joint may throw a whole system out of order. 
For this reason all joints should be soldered wherever prac- 
ticable. In line work, however, this is impossible, except 
where trolley- wires are joined, and these are brazed in the 
open air by an apparatus especially designed for the pur- 
pose. In telegraph and telephone lines perfect contact is 
absolutely necessary, and where attachments are made to 
insulators the main-line should never be turned around 
the insulator. The wire is brought up against the insu- 
lator, and with a U wire the main-line is tightly bound to 
it, as shown at Fig. 11. If it is necessary to bind the main- 
line more securely to the insulator, one or two turns may 
be taken around the insulator with the U or anchoring wire ; 
then with a pair of plyers a tight wrap is made. 

When joining two ends of wire together, never make 
loops as shown in Fig. 12 A. This construction gives poor 

304 



MISCELLANEOUS APPARATUS 

contact, for the wire loops will wear and finally break 
apart. Moreover, the rust that forms between the loops 
will often cause an open circuit and one difficult to locate. 
Care must be taken to make all splices secure and with per- 




fect contact of wires, and the only manner in which this can 
be done is to pass the ends of wires together for three or 
four inches, as shown in Fig. 12 B. 

Grasp one wire with a pair of plyers, and with the fingers 
start the coil or twist, then with another pair of plyers 
finish the wrapping evenly and snugly. Treat the other 
end in a similar manner, and as a result you will have the 
splice pictured in Fig. 12 B, the many wraps insuring per- 
fect contact. This same method is to be employed for in- 
side wires, and after the wrap is made heat the joint and 
^° 305 



ELECTRICITY BOOK FOR BOYS 

touch it with soldering solution. The solder will run in 
between the coils and permanently unite the joint. The 
bare wires should then be covered with adhesive tape. 

Avoid sharp turns and angles in lines, and where it is not 
possible to arrange them otherwise it would be well to put 
in a curved loop, as shown at Fig. 13. A represents a pole, 
B B the line, and C the quarter-circular loop let in to avoid 
the sharp turn about the insulator. The current will pass 
around the angle as well as through the loop, but a gal- 
vanometer test would show that the greater current passed 
through the loop and avoided the sharp turn. 

''Grounds*' 



In the chapter on wireless telegraphy several good 
''grounds" were described, any one of which would be ad- 
mirably adapted to telegraph or telephone circuits. In 
Figs. 14, 15, and 16 are illustrated three other "grounds" 
that can easily be made from inexpensive material. The 




TlGr.l4. 



riGri5:- 




riGr.l6.. 



306 



MISCELLANEOUS APPARATUS 

first one, Fig. 14, is an ordinary tin pan with the wire 
soldered to the middle of the bottom. The wire must be 
soldered to be of use, as the pan would soon rust around a 
simple hole and make the ''ground" a high-resistance one. 
If the pan is buried deep enough in the earth, and bottom 
up, it will last for several years, or so long as the air does 
not get at it to induce corrosion. 

The star-shaped "ground" is cut from a piece of sheet 
zinc, copper, or brass, and is about twelve inches in diam- 
eter. The wire is soldered to the middle of it, and it is 
buried four feet deep, lying flat at the bottom of the hole. 

In Fig. 16 a pail or large tin can is shown with the wire 
passing down through the interior and finally reaching the 
bottom, where it is soldered fast. The can is filled with 
small chunks of carbon, or charcoal, and some holes are 
punched around the outer edge and bottom to let the water 
out. The can is then buried three or four feet in the 
ground. Use nothing but copper wire for "grounds," and 
it should be heavy — nothing smaller than No. 14. The 
wire should be well insulated down to and below the sur- 
face for a foot or two, so that perfect action will take place 
and a complete "ground" secured. 

The Edison Roach-killer 

When Edison was a boy he invented the first electrocu- 
tion apparatus on record. At a certain station on the 
Grand Trunk Railroad, where Edison was employed as a 
telegraph operator, the roaches were so thick that at night 
they would crawl up the partition between the windows 

307 



ELECTRICITY BOOK FOR BOYS 

and reach the ceiUng, where they would go to sleep. During 
the day they were apt to become dizzy, lose their footing, 
and drop down on the heads of the operators. This did not 
suit young Edison, so he devised a scheme for their de- 
struction. While watching a piece of telegraph apparatus 
one day, he saw a roach try to step from a bar charged 
with positive electricity to one through w^hich a negative 
current flowed. The insect's feet were moist and so made 
a connection between the two bars. As a consequence a 
short-circuit of high tension passed through its body and it 
dropped dead. This put an idea into Edison's head, and 
the electrocution apparatus v/as soon in working order. 
The "killer" was the most simple device one could imagine, 
and was composed of two long, narrow strips of heavy tin- 
foil pasted side by side on a smooth board, with a space of 
one-eighth of an inch between them, as shown at Fig. 17. 
To one strip a positive wire was connected, while to the 
other a negative or ground was made fast. High-tension 
current, or that from an induction-coil, was connected with 
the wires, and the resulting voltage was strong enough to 
give one a severe shock if the fingers of one hand were placed 
on one plate and those of the other hand on the other plate. 
This device was arranged across the window-casing in 
the path the roaches were accustomed to travel on their 
nightly trips up the side wall. It was not long after dark 
before roach number one sauntered up the wall, crossed the 
under strip, and stepped over on the upper one. But he 
went no farther, and he, with many of his friends and rela- 
tions, were gathered up in a dust-pan the next morning and 
thrown into the stove. 

308 



MISCELLANEOUS APPARATUS 

In electricity, as in many other things, simplicity is the 
key-note of success; and from this little device to employ 
the alternating current for ridding a house of an insect 
nuisance sprang the grim apparatus known as the ''death 
chair," used in the execution of first-degree criminals in the 




State of New York. Many people think the mechanism for 
electrocution is a complicated one, but it is quite as simple 
as the Edison roach-killer. One pole is placed at the head 
of the criminal and the other at the feet, the latter being 
bound fast so that perfect contact can be had. Then an al- 

309 



ELECTRICITY BOOK FOR BOYS 

ternating current of fifteen hundred to two thousand volts 
is run through the body, and death is instantaneous and 
void of pain. 

An Electric Mowse-killer 

A modification of the simple roach -killer was recently 
used by the author in his laboratory to get rid of some 
troublesome mice. A piece of board was cut twelve inches 
square, the edges being bevelled so that it would be an easy 
matter for the mice to climb up on it. An inch- wide cir- 
cle of sheet brass was prepared measuring eleven inches 
outside diameter and nine inches inside. Another circle 
was cut measuring eight inches and a half outside and six 
inches inside diameter. Both circles were attached to the 
board with copper tacks and polished as bright as possible, 
the finished board appearing as shown in Fig. i8. 

Wires were soldered to each strip, and these in turn were 
connected to a high-tension current of several thousand 
volts. Crumbs and small pieces of meat were placed on the 
board inside the circles, and the trap was set in a convenient 
place on the floor of the laboratory. 

The next morning several mice lay dead on the floor, but 
at some distance from the board, and this seemed a little 
mysterious. The following night the author worked late 
in the laboratory. After finishing what he had on hand, 
he turned down the lights and sat down and watched the 
trap. Presently Mr. Mouse appeared from somewhere. 
He sniffed the air, then approached closer to the board, 
sniffed again, and, evidently concluding that he was on the 

310 



MISCELLANEOUS APPARATUS 

right trail, he climbed up the side of the board and stood 
on the outer strip. He placed one fore-foot on the inner 
strip, and, bang! up he went in the air, and landed on the 
floor a foot or more away. His jump into space was due to 
the electric action on his muscles, for the current literally 
tore his nervous system into shreds. 

Mr. Mouse lost a great many friends and relatives that 
season in the same manner, and the apparatus is confident- 
ly recommended as a certain and humane agent for the de- 
struction of all small vermin. 



Chapter XIII 

FRICTIONAL ELECTRICITY 

FRICTION AL electricity is high potential, current alter- 
nating, and of high voltage but very low amperage. 
Apart from certain uses in laboratory and medical practice, 
it is valueless. In its greater volume it is akin to the light- 
ning-bolt and is dangerous; but in its smaller volume it is 
a comparatively harmless toy. From the glass rod, or the 
amber, rubbed on a catskin to the modern static machines 
is a long jump, and the period of exploitation covers centu- 
ries of interesting experiments, most of which, however, 
have been practically useless for any commercial purpose. 

Static or frictional electricity is generated by friction 
only, without the aid of magnets, coils of wire, or arma- 
tures rotating at high speed. The simple process of the 
glass and catskin has been variously modified, until at last 
Wimshurst invented and perfected what is "known as the 
"Wimshurst Influence Machine." It is self-charging, and 
does not require ''starting." It will work all the year 
round in any climate and temperature, and is the greatest 
improvement ever made in static electric machines. 

Apart from its efficiency under all conditions, it is the * 
simplest of all machines to make, and can easily be con- 

312 



FRICTIONAL ELECTRICITY 



structed by a boy who is handy with tools, and who can 
obtain the glass and brass parts necessary in its construc- 
tion. The principal parts of an influence machine are the 
glass disks, wooden bosses, driving pulleys and crank, glass 
standards, brass arms with the spark-balls at the ends, and. 
the base with the uprights on which these parts are built up 
and held in position. 

A "Wimsharst Influence Machine 

Obtain a stiff piece of brown paper twenty inches square, 
and with a compass describe a circle twenty inches in diam- 
eter. Inside of this circle make another one fourteen inches 
in diameter, and near the centre a third circle six inches 
in diameter. Another circle four inches in diameter should 
be drawn inside of the six-inch circle, so that when the 
bosses are made fast to the glass plates they can be properly 
centred. Also mark sixteen lines radiating from the centre, 
equal distances apart, as shown in Fig. i. 

From a dealer in glass purchase two clear, white panes 
of glass eighteen inches square. Be careful not to get the 
green glass, as this is not nearly so good as the white for 
static machine construction. If it is possible to get crystal 
plate so much the better. The panes should be thin, or 
about one-sixteenth of an inch in thickness, and free from 
bubbles, wayy places, scratches, or other blemishes. 

From these panes cut two disks sixteen inches in diameter 
with a rotary cutter, as described in the chapter on Miscel- 
laneous Apparatus, page 294, and rub the edges with a 
water-stone (see chapter on Formulae, page 330.) 

3^3 



ELECTRICITY BOOK FOR BOYS 

From flat, thin tin-foil cut thirty-two wedge-shaped 
pieces four inches long. They should be one inch and a 
half wide at one end and three-quarters of an inch at the 
other, as shown at Fig. 2 A. Give each plate of glass two 
thin coats of shellac on both sides; then lay one on the 
paper pattern (Fig. i) so that the outside edge of the glass 
will lie on the largest circle. Place a weight at the middle 
of the glass to hold it in place; then make sixteen of the 
tin-foil sectors fast to the plate, using shellac as the stick- 
ing medium. But first give one side of each sector a thin 
coat of shellac, allowing it to dry; then give it another coat 
when applying it to the glass. The sectors are to be sym- 
metrically arranged on the glass, using a line of the pattern 
as a centre for each piece (as shown at A in Fig. i), and the 
fourteen and six inch circles as the outer and inner boun- 
daries. Each piece, as it is applied, should be pressed down 
upon the glass, so that it will stick smoothly, without air 
bubbles or creases. A very good plan is to lay a piece of 
soft blotting-paper over the sector and drive it down with 
a small squeegee-roller such as is used in photography, taking 
care, however, not to shift the sector from its proper posi- 
tion. When all the sectors are on, the plate should appear 
as shown in Fig. 2. After the shellac, which holds the 
sectors to the glass, is dry, run a brush full of shellac around 
the inner and outer extremities of the tin-foil strips for half 
or three-quarters of an inch in from the ends. The shellac 
will hold the sectors firmly to the glass, and will slightl}^ 
insulate them as well, thereby preventing the escape of 
electricity. Apply the remaining sectors to the other plate 
of glass in a similar manner; and as a result two disks of 

314 




DETAILS OF WIMSHURST INFLUENCE MACHINE 



315 



ELECTRICITY BOOK FOR BOYS 

glass, with the appHed strips, will be ready to mount in 
the frame. 

A hole three-quarters of an inch in diameter should be 
made in each glass plate, so that a three-eighths spindle may 
pass through them and into the bosses, so as to keep them 
in proper line. It is preferable, however, not to bore these 
holes if bosses and accurately bushed holes can be made 
in the uprights of the frame which support these disks. 

At a wood-working mill have two bosses made that will 
measure four inches in diameter at. the large end, and one 
inch and a half at the small one. They should be of such 
length that when the plates and two bosses are arranged 
in line (to appear as shown in A A at Fig. 9) they will fill 
the entire space between the uprights B B. Near the small 
end a groove is turned in each boss, so that a round leather 
belt will fit in it, as shown in Fig. 3. 

The base is made from pine, white- wood, cypress, or any 
other wood that is soft and easily worked. It is composed 
of two strips twenty -four inches long, three inches wide, 
and one inch and a quarter in thickness, and two cross- 
pieces fourteen inches long, three inches wide, and one inch 
and a half thick. 

These are put together with glue and screws, and at both 
sides of the base notches are cut to accommodate the feet 
of the uprights. The uprights are seventeen inches high, 
three inches wide, and one inch and a half thick. The 
notch at the foot of each one is cut so that, when fitted in 
place, the foot of the upright will rest on a table on a line 
with the bottom of the end cross-pieces under each corner. 
At the foot of the uprights a piece of sheet rubber should be 

316 



FRICTIONAL ELECTRICITY 



made fast, with glue or shellac, so that when in operation 
the machine will not move about or slide. 

A groove is cut at one side of each upright six inches 
above the bottom, as shown at Fig. 4 A. In this groove 
the driving-wheel axles fit, and near the top holes are made 
in the uprights through which the spindles pass, which in 
turn support the bosses and glass disks. 

At the middle of each cross-piece forming the ends of 
the base a one-inch hole, for the glass standard rods, is 
bored through the wood, as shown at Fig. 4 B B. After 
attaching the uprights to the base with glue and screws, 
and giving all the wood-work several successive coats of 
shellac, the frame will be ready for its mountings. 

The driving-wheels are of wood seven-eighths of an inch 
thick and seven inches in diameter ; they should be turned 
on a lathe and a groove cut in the edge so that a round 
leather belt will fit in it. These wheels are mounted on a 
wooden axle that can be made from a round curtain-pole, 
with a half -inch hole bored through its entire length. The 
axle is as long as the distance between uprights B B in 
Fig. 9. The wheels are to be arranged and glued fast to 
the axle, so that the grooves will line directly under those 
in the bosses, as shown in Fig. 9. A half -inch axle is 
driven through the hub, and at one end it is threaded and 
provided with two washers and nuts; or a square shoulder 
and one washer and nut may be used, so that a crank and 
handle may be held fast. Shellac should be put on the 
shaft to make it hold fast in the hub. 

The complete apparatus of wheels, axle, hub, and handle 
is shown at Fig. 5, and in the frame this is so hung that the 

317 



ELECTRICITY BOOK FOR BOYS 

iron axle rests in the grooves cut in the uprights. To hold 
this in place two metal straps, as shown in Fig. 6, are made 
and screwed fast to the wood. When finally adjusted the 
driving-wheels should rotate freely whenever the crank is 
turned. The wooden bosses, Fig. 3, are given two or three 
coats of shellac ; then they are made fast to the glass disks 
on the same side to which the tin-foil sectors are attached. 
The disks should be placed over the paper plan, Fig. i, 
and so adjusted that the outer line tallies with the large 
circle. Acetic glue^ is then applied to the flat surface of 
the boss, and the latter is placed at the middle of the disk 
to line with the small circle. Place a weight on the end of 
the boss to hold it down, and leave it for ten or twelve 
hours or until thoroughly dry. 

Both bosses should be set at the same time so that they 
may dry together. 

If the bosses are turned on a lathe a hole should be made 
in each one about half-way through from the small end. 
This, in turn, should be bushed or lined with a piece of 
brass tube, w^hich should fit snugly in the hole. A little 
shellac painted on each piece of tube will make it stick. 
Pieces of steel rod that will just fit within the tubing are 
to be cut long enough to enter the full length of the hole, 
pass through the holes made in the top of the uprights, and 
extend half an inch beyond, as shown in Fig. 9. The bosses 
and axles will then appear as shown in Fig. 7. 

Flat places should be filed on each rod where it passes 
through the wood upright; a set-screw will then hold it 

^ See Formulas, Chapter xiv., for the recipe of acetic glue. 

318 



FRICTIONAL ELECTRICITY 



fast and keep it from revolving. When the hole, or tubing, 
is oiled so that the boss and disk will revolve freely on the 
axle, the disks, bosses, and axles are ready to be mounted 
in the frame. 

A red fibre washer, such as is used in faucets, should be 
made fast to one glass disk at the centre, so as to separate 
the disks and prevent them from touching when they are 




y^ \ \ \ \ I [ iw 

" 4 « » I I i i IQ 



TiG-.^. 




revolving in opposite directions. These fibre washers can 
be had from a plumber or purchased at a hardware store. 
Shellac or acetic glue will hold the washers in place. 

Mount one disk by holding the boss with the small end 
opposite a hole in one upright, and slip an axle through 
from the outside of the upright. Hold the other disk in 
place, and slip the remaining axle through the other up- 

319 



ELECTRICITY BOOK FOR BOYS 

right and into the boss. When both plates are in place 
and centred, turn the set-screws down on the flattened axles 
to hold them in place. 

To reduce the friction between the bosses and the up- 
rights it would be well to place a fibre washer between 
them. A few drops of oil on these washers will lubricate 
them properly, and allow the machine to run easier. An. 
end view of the apparatus, as so far assembled, will appear 
as shown in Fig. 9, A being the disks, bosses, and axles, 
B B the uprights supporting them, C the hub, and D D 
the driving-wheels. The handle and crank (E) extends out 
far enough from the side to allow a free swinging motion 
without hitting the upright or base. Having arranged these 
disks and wheels so as to revolve freely, it will now be 
necessary to construct and add the other vital parts and 
the connecting links in the chain of the complete working 
mechanism. 

From a supply-house obtain two solid glass rods an inch 
in diameter and fifteen inches long. These fit in the holes 
(B B) bored in the end-pieces of the base. Fig. 4. Procure 
two brass balls, two or two and a half inches in diameter, 
such as come on brass beds, and two short pieces of brass 
tubing, one inch inside diameter, that will fit over the ends 
of the rods. These tubings are to be soldered fast to the 
balls so that both tubes and balls will remain at the top 
of the glass rods. 

From brass rod three-sixteenths or a quarter of an inch 
in diameter make two forks, as shown at Fig. 8, and solder 
small brass balls at the ends of the rods. The prongs of 
the fork are six inches long and the shank four inches in 

320 



FRICTIONAL ELECTRICITY 



length. Along the inside of the forks small holes are bored, 
and brass wires, or "points," are soldered fast. These ex- 
tend out for half an inch from the rods, and are known as 
the " comb," or collectors. The forks should be so far apart 
that when mounted with the glass disks revolving between 
them the points will not touch or scratch the tin-foil sectors, 
and yet be as close to them as possible. A hole should be 
bored in the brass balls, and the shank of the fork passed 
through and soldered in place, as show^n in Fig. lo. 

A three-eighth-inch hole is bored directly in the top of 
each brass ball to hold the quadrant rods, which extend 
over the top of the disks. ^ 

In the illustration of the complete machine (Fig. 12) the 
arrangement of the glass pillars, balls, combs, and quadrant 
rods is shown. The rods are three-eighths of an inch in 
diameter and are loose in the holes at the top of the balls, 
so that they can be moved or shifted about, according as to 
whether it is a left or a right handed person who may be 
turning the crank. 

At the upper end of each rod a brass ball is soldered, one 
being three-quarters of an inch in diameter, the other two 
inches. The projecting ends *of the forks should be pro- 
vided with metal handles or brass balls, as shown in Fig. 12 ; 
these may be slipped over the end or soldered fast. Obtain 
two small brass balls with shanks, such as screw on iron 
bed-posts, and have the extending ends of the axles that 
support the bosses threaded, so that the balls will screw 
on them. Bore a quarter-inch hole through each ball, and 
slip a brass rod through it and solder it fast. Each end of 
these rods should be tipped with a bimch of tinsel or fine 
21 321 



ELECTRICITY BOOK FOR BOYS 



copper wires. These are the "neutraHzers," and the ends 
are curved so that the brushes of fine wires will just touch 
the disks when the latter are revolved, as shown in Fig. 12. 




The ball holding the rod is to be screwed fast to the axle; 
then the axle is pushed back into the boss and made fast 
in the head of the upright with the set-screw. 

322 



FRICTIONAL ELECTRICITY 



The rod - and - ball at the opposite side of the disks is 
arranged in a similar manner, but the rod points in an 
opposite direction to that on the first side. Cord or leather 
belts connect the driving-pulleys and bosses, the belt on 
one side running up straight over the boss and down again 
around the driving-pulley. The belt at the opposite side 
is crossed, so that the direction of the boss is reversed ; and 
in this manner the disks are made to revolve in opposite 
directions, although the driving-pulleys are both going in 
the same direction. 

A portion of the sectors are omitted in the illustration 
(Fig. 12) so that a better view of the working parts may be 
had. When the disks are revolving the accumulated elec- 
tricity discharges from one ball to the other, above the 
plates, in the form of bright blue sparks sufficiently power- 
ful to puncture cardboard if it is held midway between 
the balls. 

A Large Leyden-jar 

When experimenting with this machine it would be well 
to have one or more Leyden - jars to accumulate static 
charges. A large one of considerable capacity is easily 
made from a battery jar, tin-foil, brass rods and chain, and 
some other small parts. 

Obtain a blues tone battery jar, and after heating it to 
drive all moisture from the surface, give it a coat of shellac 
inside and out. With tin-foil, set with shellac, cover the 
bottom and inside of the jar for two-thirds of its height 
from the bottom, as shown in Fig. 11. Cover the outside 
and bottom in a similar manner, and the same height from 



ELECTRICITY BOOK FOR BOY S 

the bottom, and provide a cork, or wooden cap, for the top. 
If a large, flat cork cannot be had, then make a stopper 
by cutting two circular pieces of wood, each half an inch 
thick, the inner one to fit snugly within the jar, the other 
to lap over the edges a quarter of an inch all around. Fas- 
ten these pieces together with glue, as shown at Fig. 13, 
and give them several good coats of shellac. Make a small 
hole at the middle of this cap and pass a quarter-inch rod 
through it, leaving six inches above and below the cap. 
To the top of the rod solder a brass ball. At the foot a piece 
of brass chain is to be made fast, so that several links of it 
rest on the tin-foil at the bottom of the jar. 

To charge a jar from the Wimshurst machine, stand the 
jar on a glass-legged stool, and connect a copper wire be- 
tween one of the overhead balls on the machine and the ball 
at the top of the rod in the stopper of the jar. Make an- 
other wire fast to the other ball at the top of the machine, 
and place it under the jar so that the tin-foil on the bottom 
touches it. By operating the machine the jar is charged. 

To discharge the jar make a J-yoke, as shown at Fig. 14, 
by nailing a brass rod fast to a wooden handle and soldering 
brass knobs, or hammering a lead bullet, on the ends of the 
rod. Hold one knob against the top knob of the jar and 
bring the other near the foil coating at the outside, when 
a spark will jump from the, foil to the knob with a loud 
snap. 

A Glass-legged Stool 

One of the most useful accessories in playing with fric- 
tional electricity will be a glass-legged stool. A stool with 

324 



FRICTIONAL ELECTRICITY 





flG:l3 



TIG-.II. 





ri&.i4- 




riG-. 16 . 



glass feet is perhaps too expensive for a boy to purchase, 
but one may be made at httle or no cost from a piece of 
stout plank, four glass telegraph line-insulators, and the 
wooden screw-pins on which they rest when attached to a 
pole. 

The general plan of the stool is shown at Fig. 15, and 
the top measures twelve by fifteen by two inches. Under 
each corner a screw-pin is made fast by boring a hole in 

325 



ELECTRICITY BOOK FOR BOY S 

the wood and setting the pin in glue. The pins are cut 
at the top, as shown in Fig. i6, and when they are set in 
place the glass insulators may be screwed on. The wood- 
work should be given a few coats of shellac to lend it a good 
appearance and help to insulate it. 

There are a great many interesting experiments that 
ma}^ be performed with static or frictional electricity, and 
these may be looked up in the text-books on electricity 
used in school. A word of caution will not be misplaced. 
Remember that the current, in large volume, is dangerous. 
For example, a series of charged Leyden-jars may contain 
enough electricity to give a very severe shock to the nervous 
system of the person who chances to discharge it. Its 
medical use should be under the advice and supervision of 
a physician. 



Chapter XIV 

FORMULA 

IN the construction of electrical apparatus there are 
many things, such as paint, cement, non-conducting com- 
pounds, and acid-proof substances, that are necessary in 
assembling the parts which make up complete working 
outfits. Accurate formula and directions for these things 
will save the amateur trouble and expense, since they in- 
dicate the materials which have been put to the test of time 
and wear by others who have had abundant experience 
along these lines. 

The amateur will not need a large number of compounds, 
but such as are necessary should be of the best. Those 
which are described in this chapter can be relied upon to 
give working results. 

Acid-proof Cements 

One of the best acid-proof cements is made by adding 
shellac, dissolved in grain alcohol, to red-lead until it is at 
the right consistency. It can be used in liquid form or 
in a putty-like paste. The consistency is governed by the 
amount of shellac added to the red-lead. The lead should 
be pulverized and free from lumps. This cement 'can be 

327 



ELECTRICITY BOOK FOR BOYS 

mixed in a small tin cup or on a piece of glass, with a knife 
having a thin blade. 

It should be used as soon as it is mixed, since it "sets" 
as quickly as shellac, and then dries from the outside to- 
wards the middle. In a week or two it will become dry 
and hard like stone. 

Another cement, which will also dry as hard as a stone 
and will hold soapstone slabs together as if they were of 
one solid piece, is made of litharge (yellow lead) and glyc- 
erine. The glycerine is added to the pulverized litharge 
to make a paste, or it can be mixed and kneaded like thin 
putty. It should be used very soon after mixing, as it sets 
rapidly. 

Hard Cement 

A medium hard cement is made from plaster of Paris, 
six parts; silex, or fine sand, two parts; dextrine, two parts 
(by measure). Mix with water until soft; then work with 
a trowel or knife. 

Soft Cement 

A good soft cement is made of plaster of Paris, five parts ; 
pulverized asbestos, five parts (by weight). Add water 
enough to make a soft paste, and use with a trowel or knife. 
This is a heat-proof compound and is commonly know^n as 
asbestos cement. 

Very Hard Cement 

One of the hardest cements that can be made is com- 
posed of hydraulic cement (Portland or Edison), five parts; 

328 



FORMULA 



silex, or white sand, five parts (by measure). Mix with 
Water and use Hke plaster with a trowel or spatula. 

Care must be taken when the parts are combined to see 
that the cement is free from lumps. These must be broken 
before the silex, or sand, and water are added. Then the 
two parts should be mixed together at first and moistened 
afterwards. The proper way is to place some water at the 
bottom of a pan; then add the dry mixture by the hand- 
fuls, sprinkling it around so that the water can enter into 
it without forming lumps. Keep adding and mixing until 
the mass is at the right consistency to work. 

All these cements are acid-proof. 

Clark's Compound 

For exterior insulation, where the parts are exposed to 
the weather, a superior compound is made up of mineral 
pitch, ten parts ; silica, six parts ; tar, one part (all parts by 
weight). This is called Clark's compound, after the man 
who invented it and used it successfully. 

It is heated, thoroughly mixed, and used with a brush 
or spatula. 

Battery Fluid 

A depolarizing solution for use in zinc-carbon batteries 
like the Grenet is composed as follows : 

Dissolve one pound of bichromate potash or soda in ten 
pounds of water (by weight). When it is thoroughly dis- 
solved add two and one - half pounds of sulphuric acid, 
slowly pouring it into the bichromate solution and stirring 

329 



ELECTRICITY BOOK FOR BOYS 

it with a glass rod. The addition of the acid will heat the 
solution. Do not use it until it has entirely cooled. 

Glass Rubbing 

To rub the edges of glass, such as the disks for Wimshiirst 
machines, obtain a piece of hard sandstone, such as is used 
for sharpening knives or scythes. The glass is placed on a 
table so that the edge extends beyond. Oil of turpentine 
is rubbed or dropped on the surface of the stone, and the 
edge of the glass is moistened with a rag soaked in the tur- 
pentine. Hold the glass down securely with one hand, and 
with the other grasp the stone and give it a forward and 
backward motion, grinding the glass along its edge and not 
crosswise. With care and patience a rough edge can soon 
be brought to a smooth one, and a soft, rounded corner sub- 
stituted for the hard, angular, cutting edge that makes the 
glass a difficult thing to handle. Use plenty of lubricant in 
the form of oil of turpentine to make the work eavSy. 

Acetic GItte 

One of the best glues for glass and wood or glass and 
fibre is made by placing some high-grade glue (either flake 
or granulated) in a cup or tin and covering it with cold 
water. Allow it to stand several hours until the glue ab- 
sorbs all the water it will and becomes soft; then pour the 
water off, and add glacial acetic acid to cover the glue. The 
proportion should be eighteen parts of glue to two of acid. 
Heat the mass until it is reduced to liquid, stirring it until 

330 



FORMULA 



it is thoroughly mixed. When ready for use it should be 
poured into a bottle and well corked to keep the air away 
from it. 

Insulators 

Apart from glass and porcelain, insulators can be made 
from non-conducting compounds, the best of which is 
molded mica. Ground mica or mica dust is mixed with 
thick shellac until it is in a putty-like state. It may then 
be forced into oiled molds of any desired shape. Hydraulic 
pressure is employed for almost every form of molded 
mica that is made for commercial purposes; but as a boy 
cannot employ that means to get the best results, he must 
use all the pressure that his hands and a flat board will 
give. 

Another compound is made from pulverized asbestos 
and shellac, with a small portion of ground or pulverized 
mica added, in the porportion of asbestos, six parts ; mica, 
four parts. Shellac is added to make a pasty mass, which 
is kneaded into a thick putty and forced into oiled molds 
until it sets. It is then removed and allowed to dry in the 
open air, and the mold used for more insulators. 

Non-condttctors 

When working in different materials that seem adapted 
to electrical apparatus, it is necessary to know whether they 
can be used safely or not. Often a material seems to be 
just the thing, but if it should be a partial conductor, when 
a non-conductor is desired, it would be hazardous to use 

331 



ELECTRICITY BOOK FOR BOYS 

it. A list of non-conductors is therefore valuable to the 
amateur. Some of the principal non-conductors, among 
the many, are as follows: glass, porcelain, slate, marble, 
hard stone, soapstone, concrete (dry), hard rubber, soft rub- 
ber, composition fibre, mica, asbestos, pitch, tar, shellac, 
cotton, silk; cotton, silk and woollen fabrics, transite (dry), 
electrobestus (dry), duranoid; celluloid, dry wood (well sea- 
soned), paper, pith, leather, and oil. 

While this account of formulas and material might be ex- 
tended, this is not necessary inasmuch as the formulas and 
practical directions which have been given will answer all 
usual practical requirements. 



Insulating Varnish 

There are several good insulating varnishes that can be 
used in electrical work, the most valuable being shellac dis- 
solved in alcohol and applied with a brush. To make good 
shellac, purchase the orange -colored flake shellac by the 
pound from a paint-store, place some of it in a wide-necked 
bottle, and cover it with alcohol; then cork the bottle and 
let it stand for a few hours. Shake the bottle occasionally 
until the shellac is thoroughly dissolved. It can be thinned 
by adding alcohol. Always keep the bottle corked, taking 
out only what is necessary from time to time. 

Another varnish can be made by dissolving red sealing- 
wax in alcohol and adding a small portion of shellac. This 
can be applied with a soft brush, and is a good varnish. 
When colors are to be applied to distinguish the poles, red 

332 



FORMULiE 



is used for the positive current-poles and blue or black for 
the negative, if they are colored at all. 

A very good black varnish is made by adding lampblack 
to shellac; another consists of thick asphaltum or asphal- 
tum varnish. This is waterproof, and dries hard, yet with 
an elastic finish. 

Battery Wax 

For the upper edges of glass cells, such as the Leclanche 
or other open -circuit batteries, there is nothing superior to 
hot paraffine brushed about the upper edge to prevent the 
sal-ammoniac or other fluids from creeping up over the top. 
The parafline can be colored with red-lead, green dust, or 
powders of various colors if desired, but generally the paraf- 
fine is used without color, so that it has a frosted-glass ap- 
pearance when it is cool and dry. 

A black wax for use in stopping the tops of dry cells 
and coating the tops of carbons is composed of paraf- 
fine, eight parts; pitch, one part; lampblack, one part. 
Heat the mixture and stir it until thoroughly mixed; 
then apply with a brush, or dip the parts into the warm 
fluid. 

Another good black wax is composed of tar and pitch in 
equal parts. They are made into a pasty mass with tur- 
pentine heated over a stove, but not over an open flame, 
because the ingredients are inflammable. The compound 
should be like very thick molasses, and can be worked with 
an old table-knife. 



Chapter XV 

ELECTRIC LIGHT, HEAT, AND POWER 

WITH the discovery of the reversibility of the dynamo, 
the invention of the telephone, and the improvements 
in the electric light began the great modern development 
of electricity which proved that marvellous agent to be a 
master- workman. 

Many of the things electrical that we ordinarily think of 
as modern inventions are merely modern applications of 
phenonema that were discovered many years ago. The 
pioneers in the science of dynamic electricity performed 
their experiments with the electric light, electro-magnets, 
etc., by using galvanic batteries. But for practical pur- 
poses the consuming of zinc and chemicals in such batteries 
was too expensive a way to generate electricity, and pre- 
vented any commercial use of the results- of their experi- 
ments until cheaper electricity could be had. 

The "Work of the Dynamo 

The invention of the dynamo, with which we obtain elec- 
tricity from mechanical power, changed all that. Instead 

For the use of the cuts in this chapter, the Publishers desire to acknowl- 
edge the courtesy of the General Electric Company, the Thomson Elec- 
tric Welding Company, and the Cooper Hewitt Electric Company. 

334 



ELECTRIC LIGHT 



of consuming zinc in primary batteries, men could obtain it 
by burning coal, which is much cheaper, under the boiler of a 
steam-engine used to drive the dynamo. Thus it is that 
modern electricity comes from mechanical power. It is 
really the energy of a steamx-engine or a water-wheel, or some 
other "prime mover," working through the medium of 
electricity, that is transmitted to a distance and distributed 
over wires. The electricity may then be tra.nsmuted into 
light, heat, or chemical energy as the case may be, to light 
our electric lamps, develop the intense heat of the electric 
furnace, and charge storage-batteries. 

Moreover, some time after the invention of the dynamo 
it was found that the mechanical power put into one of 
these machines could be transmitted electrically and re- 
produced as mechanical power. In other words, a dynamo 
could be made to revolve and give out power, as a motor, 
by supplying it with current from another dynamo. This 
showed the way to transmute electricity back again into 
mechanical power, to run our electric cars and trains, and 
all kinds of machinery in our factories and elsewhere. Now- 
adays the dynamo is used to generate nearly all the elec- 
tricity that we need. Even in such comparatively old 
electrical applications as electro - plating and the tele- 
graph and telephone, primary batteries are being sup- 
planted by motor dynamos, which we shall learn about 
later. 

It is from the invention of the dynamo and the discover}^ 
that it was reversible that we date the beginning of what are 
known as heavy electrical engineering applications, includ- 
ing electric light, heat, and power. In this closing chapter it 

335 



ELECTRICITY BOOK FOR BOYS 

is purposed to learn a little about these applications; and in 
so doing to summarize briefly the things that we have al- 
ready studied. 

The Electric Light 

In the chapter on Electrical Resistance we learned that 
an electric current always encounters a resistance in passing 
through a conductor, and that when the current is strong 
enough the conductor is heated up. The electric light is 
produced by the heating of a conductor of one kind or an- 
other to incandescence by the electrical friction of the cur- 
rent passing through it. 

The first electric light w^as made by Sir Humphry Davy 
over a hundred years ago. He discovered that when a 
current from a great many cells of battery was interrupt- 
ed the spark did not simply appear for an instant and 
then go out, as it does when only a few cells are used, but 
remained playing between the terminals of the circuit. He 
found by experiment that if pieces of carbon are used as 
the terminals — or "electrodes," as they are called — the 
electricity passes between them in an intensely hot flame, 
or "arc." The latter, which is due to the electrical re- 
sistance of the vapor of carbon, heats up the carbon-points 
so that they give a brilliant white light. 

Before the dynamo came into use, the electric light was 
rarely seen, except as a philosophical experiment; but as 
soon as cheap electricity became available, commercial 
electric arc-lamps were made by many inventors and have 
been continually improved. Fig. i shows one form of mod- 
ern arc-lamp, with its case removed to show the interior 

336 



ELECTRIC LIGHT 



mechanism. In m.ost arc-lamps the lamp itself consists of 
a pair of carbon or other electrodes in the form of long rods 
arranged vertically, with their tips normally in contact. 





Fig. 1 Fig. 2 

When the current is turned on, the mechanism lifts the up- 
per electrode away from the lower one. The interruption of 
the circuit thus caused "strikes the arc" between the tips, 

337 



y 



ELECTRICITY BOOK FOR BOYS 

and the mechanism keeps the arc-distance unchanged as the 
carbons burn away. Some arc-lamps are made to burn on 
continuous-current, and others on alternating-current cir- 
cuits. When continuous current is used, the upper (or 
positive) carbon burns away about twice as fast as the lower 
one, forming a cup, or "crater," from which most of the 
light comes. 

Uses of the Arc-Light 

The first commercial use of the arc-light on a large scale 
was for street-lighting, to replace the old-fashioned gas- 
lamps. But another important use is in search-lights, in 
which the arc-lamp is fitted with a powerful reflector for 
throwing a very bright light to a distance. Fig 2 is a view 
of a search-light arranged to go on top of a ship's pilot-house. 
In war-time the ships carry search-lights to help them find 
the enemy's ships and repel attack; and they are used in the 
army also, by having a portable dynamo and engine drawn 
by horses. The arc is also employed in projectors for lect- 
ure-rooms, and sometimes for the headlights of steam and 
electric locomotives and interurban electric cars. 

Incandescent and Other Lamps 

The arc-lamp came into wide use for lighting large spaces 
like streets, stores, and public halls, but was found to be too 
intense for lighting smaller places like private houses. After 
many experiments, Edison succeeded in subdividing the 
electric light into the small pear-shaped "incandescent" 
lamips that we now see everywhere. In this kind of electric 

33^ 



ELECTRIC LIGHT 



lamp the light comes from a thin " filament" of carbon, con- 
tained in a glass globe from which all air has been removed. 
Since there is no oxygen to support combustion, the fila- 
ment may be heated white-hot by the current without being 
consumed. 

In certain other forms of incandescent lamps that are 
just coming into use, the filaments are made of rare metals 
— osmium, tantalum, etc. — that will stand a high tempera- 




ELECTRICITY BOOK FOR BOYS 

ture without melting. The Nernst lamp has a filament 
consisting of a mixture of certain materials that has to be 
heated before it will conduct electricity. 

Then there are the so-called "vapor" lamps, consisting of 
a glass tube full of conducting metallic vapor which gives 
out light when a current is passed through it. The best- 
known form is the Cooper Hewitt mercury vapor -lamp 
shown in Fig. 3, which gives a peculiar greenish light. 

From the point of view of efficiency, the electric light, 
wonderful as it is, leaves much to be desired. The light 
always comes from a hot resistance; and whether this re- 
sistance is a mass of conducting vapor, as in the arc and 
vapor lamps, or a solid conducting filament, as in the so- 
called "incandescent" lamps, much more heat than light 
is produced. A needed improvement, therefore, is in the 
direction of obtaining a greater percentage of light for a 
given amount of electrical energy. 

Electric Heat 

The generation of heat in electrical devices usually means 
wasted energy — sometimes a very serious waste, as we have 
just seen. There are certain kinds of electrical apparatus, 
however, that are designed to transform all of the electrical 
energy delivered to them into heat, for various industrial 
and household purposes. 

Electric Furnaces 

By far the most important application of electric heat, as 
such, is in electric furnaces, by means of which we attain the 

340 



ELECTRIC HEAT 



highest temperatures known to man. The electric furnace 
consists of a chamber of "refractory" material, containing 
the substances to be acted upon by the heat, with a pair of 
big carbon electrodes thrust into the centre, as shown in 




Fig. 4 

Fig. 4, which is a picture of Moissan's electric furnace for 
the distillation of metals, and supplied with heavy continu- 
ous or alternating currents. The apparatus is therefore a 
sort of gigantic electric arc-lamp, so enclosed that the whole 
of the intense heat of the arc is confined and concentrated 
on the sm.elting or other work. In many places where cheap 
electric power is to be had — as in the vicinity of the great 
Niagara Falls power-plants— electric furnaces are em.ployed 
in what are known as electrometallurgical and electrochemi- 

341 



ELECTRICITY BOOK FOR BOYS 

cal manufacturing processes. By their aid many metals and 
other substances that were formerly scientific curiosities, or 
entirely unknown, are produced commercially; such as alu- 
minum, certain rare metals, and calcium carbide, from 
which that wonderful illuminant, acetylene-gas, is obtained. 

Welding Metals 

Another useful application of electric heat is in the weld- 
ing of metals. Instead of heating the pieces to be welded 
in a forge, their ends are simply butted together and the 
electricity — generally from an alternating-current trans- 
former — turned on. The heat developed by the "contact 
resistance" between the pieces quickly softens the metal so 
that the pieces may be forced' together, forming a perfect 
weld in a few minutes without any hammering. Fig. 5 is 
a view of one form of electric welding-machine in which this 
is accomplished. The electric process can weld certain 
metals that cannot be joined securely by ordinary welding 
methods, and is used in several special arts. 

Welding is also performed by the heat of a special electric 
arc-lamp, which a workman holds in his hand like a blow- 
pipe or torch. This process is especially useful in joining the 
edges of sheet-steel, in making tanks for electric "trans- 
formers," etc. The workmen have to wear smoked glasses 
in order to protect their eyes from the intense glare of the 
arc. 

Electric Car-heaters 

Perhaps the simplest and best-known application of electric 
heat is the electric car-heater, consisting of coils of high- 

342 



ELECTRIC HEAT 



resistance wire — such as iron or German-silver wire — mount- 
ed on an insulating, non-combustible frame which is placed 
under the seats of the car. Part of the current from the 




Fig. 5 



trolley wire or third rail passes through the resistance- 
coils, heating them up and thereby warming the air in the 
car. 

343 



ELECTRICITY BOOK FOR BOYS 



Household Uses 

Nowadays electric heat is being more and more widely 
utilized in what are known as household electric heating- 
appliances. One of the most useful of these is the electric 
flat-iron, shown in Fig. 6. This flat-iron is designed to do 
away with the use of a hot stove of any kind, and is inter- 
nally heated by means of a resistance-coil of peculiar shape 
placed in the bottom of the iron close against its working 
face. The iron is connected to an electric-light socket by 
means of an attaching plug on the end of a long, flexible 
cord. It takes only a few miinutes to get hot, and. its use 
saves much time and labor. 

The list of special heating- appliances that are now made 
includes curling-iron heaters; heating-pads, for taking the 
place of hot- water bags in the sick-room; cigar-lighters, in 
which a little grid ''resistance" is made incandescent by 
pressing a button; foot- warmers; and radiators to dry wet 
shoes or skirts on rainy days. For industrial use there are 
glue-pots, for bookbinders and X-^attern-m.akers ; large flat- 
irons, for tailor-shops and laundries ; and electric ovens, for 
drying certain parts of electrical machines and for cooking 
various kinds of "prepared foods." 

Many electric cooking-utensils are made for the household, 
such as coffee-percolators, egg-boilers, ovens, disk stoves, etc. 
Each one is equipped with a resistance-coil like that in the 
electric flat-iron just described, so that it contains its own 
source of heat, which is under perfect control by means of a 
switch. An " electric kitchen " consists of a number of these 

344 



ELECTRIC POWER 



utensils, wired to a convenient table or stand, as shown in 
Fig. 7. 

Electric Power 

We have seen that the modern way to generate electricity 
is from mechanical energy applied through a dynamo, and 
that the "electric powder" thus generated may be trans- 




Fig. 6 





..^-v-.rr^^^^^^^^^^^^^^^^^^^ llljira... ...:_..: 






bi'-iii^^^^H 












f^ffl^^^ 


^ 

^ 


m 







Fig. 7 



mitted over wires to a distance and there transformed into 
other forms of energy, such as light, heat, and chemical en- 
ergy, or reproduced again as mechanical energy. The last 
mentioned of these transformations is the most important of 
them all, because it is the one that means the most for the 
advancement of civilization. Before the invention of the 

345 



ELECTRICITY BOOK FOR BOYS 

dynamo and the discovery that it was reversible, mechanical 
power could be employed only in the place where it was 
generated, so that its use was restricted ; whereas nowadays 
the field of power is broadened and its cost reduced by 
electrical transmission and distribution. 

In the chapter on Dynamos and Motors we learned how to 
make and use those machines. Let us review, very briefly, 
just what happens in the double transformation — of mie- 
chanical energy into electricity and then back again at the 
end of a line of wires — that we call electric-power trans- 
mission. In the dynam^o, the power of the water-wheel, or 
whatever other prime mover is used, is exerted in generating 
electricity by forcing the electric conductors of the machine 
thi'ough a magnetic field. The electricity is led away to a 
distance — a hundred miles, perhaps — ^by wires and allowed 
to enter another machine similar to the dynamo, but operat- 
ing as a motor. Here the first process is reversed : the elec- 
tricity passing through the conductors of the motor reacts 
upon its magnetic field, causing the machine to revolve and 
thus generating mechanical power again. The line - wires 
carry the power just as positively as though a long shaft ran 
from the prime mover to the receiving end of the line, and 
much more economically. The action that goes on is 
similar to the operation of the telephone — which is indeed a 
special case of electric-power transmission — as already ex- 
plained in a former chapter: the sound of the voice being 
transformed, at the telephone-transmitter, into electrical 
energy in the form of alternating currents, then carried 
as such over the line and finally reproduced as sound again 
at the receiver. 

346 



ELECTRIC POWER 



Power from Water-wheels 

''Hydro-electric "transmissions — i.e., electric transmis- 
sions of power from a water-wheel as prime mover — are the 
most important because they bring into use cheap water- 
power that formerly ran to waste. There are many hydro- 
electric transmissions in this country, Mexico, and Canada, 
some of themi utilizing the power of waterfalls or rapids 
located in mountainous and inaccessible parts. The al- 
ternating current is nearly always used because by it men 
can much more easily and safely generate, transmit, and 
receive the high voltages that have to be used than by the 
continuous current. The m.achinery at the ''main generat- 
ing station" consists of big alternating - current dynamos, 
which sometimes have vertical shafts instead of horizontal 
ones, so that they may be driven directly by turbines. 
The current is generated at a . mioderate potential, which 
is then "stepped -up," by "static transformers," to the 
comparatively high -line voltage that is required in long- 
distance transmissions. 



Transformers 

Fig. 8 is a view of a very large transformer of over 2500 
electrical horse-power capacity. In the picture the contain- 
ing-tank is represented as transparent, so as to show the 
transformer proper inside. The latter is really a special kind 
of induction-coil, with primary and secondary windings, and 
a core, weighing many tons, built up of thin sheets of steel. 
In this kind of transformer, the tank is filled with oil, to 

347 



ELECTRICITY BOOK FOR BOYS 




I 



Fig. 8 

keep the transformer cool in operation, and to help insulate 
it against the high potential to which it is subjected. At 
the receiving end, or '' sub-station," the high-voltage electric 

348 



ELECTRIC POWER 



power enters a set of "step-down" transformers, from which 
it is deHvered again, at moderate potential, to the mo- 
tors. 

Sometimes power is distributed from a single great gen- 
erating station to several sub-stations. In the Necaxa 
transmission, in Mexico, over 35,000 horse-power is taken 
from a waterfall in the mountains and transmitted at 60,- 
000 volts potential to Mexico City, 100 miles away, and 
to the mining town of El Oro, seventy -four miles far- 
ther on. 

Several kinds of motors are used at the receiving end of 
electric-power transmission-lines, according to the work that 
they are called upon to do. For "stationary" work, like 
driving the machines in mills and factories, two principal 
kinds of alternating - current motors are employed — syn- 
chronous and induction motors. The former are built just 
like alternating- current dynamos, and when they are run- 
ning they keep " in step" with the dynamio at the other end 
of the line; i. e., the motion of their field windings relatively 
to their armatures keeps exact pace with the same motion 
at the dynamo, just as though a long shaft ran from one 
machine to the other instead of the electric wires of the trans- 
mission-line. A motor of this type, at work driving an air- 
compressor, is shown in Fig. 9. The induction-motor is 
really a sort of transformer, the prim.ary winding of which 
is the fixed part, or field, and the secondary winding the 
rotating armature. It does not keep in step with the dy- 
namo, like the synchronous motor, but adapts its speed to 
the "load," or amount of work that it is called upon to do, 
like a continuous-current motor. 

349 



ELECTRICITY BOOK FOR BOYS 

Rotary Converters 

Sometimes alternating - current electric power is trans- 
formed at the sub-station into continuous-current power. 
This is done by a special kind of transformer called a "ro- 
tary converter." The static transformers of which we have 
just been speaking are built, like ordinary reduction-coils, 
with no moving parts, and operate by taking in alternating 




Fig. 9 

currents at a given potential and giving out alternating 
currents at a different potential, higher or lower as the case 
may be. The rotary converter, however, is built something 
like a dynamo, with a stationary field and a revolving arma- 
ture, and ordinarily operates by receiving an alternating 
current at a given potential and delivering a continuous 
current of the same or a different potential. This kind of 
transformation is employed wherever it is desired to ob- 
tain any large amount of continuous current from an alter- 

350 



ELECTRIC POWER 



nating-current transmission-line; and especially to obtain 
" 500- volt continuous current" for operating street and in- 
terurban electric railways, as we shall see under the next 
heading. Fig. 10 shows one form of rotary converter built 
for supplying continuous current for trolley service. 

Oftentimes the sub-station of a transmission system con- 
tains both static transformers and rotary converters, to 
supply both alternating current and continuous current 
from the same high- voltage alternating-current line. When 
the continuous current has to be transformed from one 
voltage to another, a "motor dynamo" is used, consist- 




ELECTRICITY BOOK FOR BOYS 

ing of an electric motor driving a dynamo on a common 
shaft. 

One of the most interesting features of electric - power 
transmission is the care that is taken to avoid the terrible 
danger from the high potentials, and at the same time pre- 
vent loss of power on the way. The electricity in the ma- 
chinery and in the line- wires that extend across the coun- 
try is veritable lightning, and has to be carefully guarded 
from doing any damage or escaping. To prevent leakage, 
the insulation of all of the station machinery an^ appara- 
tus is made extra good, with "high dielectric strength," so 
that it will not be punctured by the high voltage; and the 
line - insulators are made very large, and electrically and 
mechanically strong — quite unlike the ordinary-sized glass 
or porcelain insulators that are employed for telegraph and 
telephone lines. Each insulator before being put up is 
tested under a "breakdown voltage" much higher than it is 
to stand in actual service. 

Oil-switches 

The switching of high-voltage electric power is a knotty 
problem. The circuit cannot be interrupted by " air-break" 
switches, such as are used in ordinary electric - light sta- 
tions, for any attempt to do so would result in a destruc- 
tive arc many feet long, that could not be extinguished. 
Therefore "oil-switches" are always used to control the 
line-circuits at the main generating station and the sub- 
stations. In these oil-switches — which are designed to be 
operated from a distance, by hand -levers, or sometimes 
by electric motors — the circuit is made and broken under 

352 



ELECTRIC POWER 



the surface of oil, which prevents the formation of an arc. 
Moreover, the switchboard attendant does not have to come 
anywhere near the deadly high- voltage wires, but can make 
the necessary connections at a safe distance. 

Electric Traction 

The use of the electric motor to propel vehicles of all 
kinds is called electric traction. It is, of course, a branch 
of electric power, which we have just been considering; and 
it is in many respects the most important branch. The 
wealth of a country is largely built up and maintained by 
its facilities for transportation, such as its canals, highways, 
railroads, and street and interurban car-lines. 

In this field electric power is playing a most important 
part, although it was not many years ago that the first 
experimental electric cars were put in to replace horses on 
the street-railways of our cities. The change was found to 
be so successful that the field of the trolley-car was widened 
and extended very rapidly, until now we have our great 
suburban and interurban electric railways, with cars almost 
or quite as big as those on the steam-railroads and running 
at even higher speeds. During the last few years, also, the 
sphere of the steam - railroad itself has been invaded by 
electricity, by the construction of powerful electric locomo- 
tives to draw passenger and freight trains. 

The Trolley-car 

Let us consider just what it is that makes a trolley-car go 
Since electric power is only mechanical energy in another 
^3 353 



ELECTRICITY BOOK FOR BOYS 

form, we know that the motionless copper trolley- wire, sus- 
pended over the track in our streets, is the means of pro- 
pelling the car just as truly — ^though in a different way — 
as if it were a moving steel cable to which the car was 




Fig. 11 



attached. We must keep in mind the fact that the elec- 
tricity is not itself the source of power, but only the medium 
of transmission. The engine in the power-house, by turning 
a dynamo there, maintains a constant electric pressure, or 
"constant potential," as it is termed, in the trolley- wire. 
This pressure of electricity forces the power through the 
motors of the car as soon as the motorman makes the 
connection to them by turning the handle of his "con- 
troller." 

354 



ELECTRIC POWER 



The Contin«o«s-ctjrrent Motor 

Fig. II is a view of one form of continuous-current motor. 
There is not much of the motor itself to be seen, because it 
is entirely enclosed in a cast-iron case. The shaft of the 
motor has a small "spur gear" fixed on one end, driving a 
gear-wheel which is fixed on the car axle. By this arrange- 
ment more than one revolution of the motor armature is 



,S»l^ 




l«S^-i^ 


■t:|f^^ 


^i 


Willl"i'>"R^||HfSS|IHB 




E 


6S 


1 

i 


Sh 




lift^R^^B 




***^B^M 


i-M^^^B 


11 


^^Hl 






PI 




t*s^Cf^ ■'^ 



Fig. 12 

355 



ELECTRICITY BOOK FOR BOYS 

required to make one revolution of the car- wheel, which 
multiplies the force exerted in turning the wheel. 

The Controller 

Fig. 12 is a view of a type of controller that is used on the 
platform of trolley-cars. The cover is removed to show the 
contacts, inside, by which the electric power is turned on 
gradually by the controller handle. The trains of electric 
cars that run on the elevated structures and in the subways 
of our large cities are supplied with power from a "third 
rail" placed by the side of the track, on insulating supports, 
and the motors on all the cars are controlled from a single 
"master-controller" on the front platform of the forward 
car. This system of control, known as the "multiple-unit" 
system, gives electric trains several advantages over the 
old kind, drawn by steam-locomotives; such as they used 
to have on the New^ York elevated roads, for example. For 
one thing, the train can be started much more quickly, 
since all the motors begin to turn the car- wheels at the same 
instant. Then again, the system, enables a long train of cars 
to be controlled as easily as a single car, and better "trac- 
tion" between wheels and track is obtained. 

Electric Locomotives 

Several of the great steam-railroads are now adopting the 
electric locomotive to draw their trains. Fig. 13 is a view 
of one of the great continuous current electric locomotives 
that are used by the New York Central Railroad to handle 
many of its passenger-trains in and out of the Grand Central 

356 



I 



ELECTRIC POWER 



Station, in New York city. The motors of this powerful 
electric engine, unlike those of trolley-cars, are "gearless"; 
that is, their armatures are fixed directly on the locomotive 
axles so that they revolve at the same speed as the driving- 
wheels. 

All of the railway motors considered thus far have been 
of the continuous- current type, although the current to 
operate them is often obtained from alternating current 




Fig. 13 

transmission-systems, through rotary converters, as de- 
scribed above. The alternating current is also beginning to 
be employed to drive cars and trains. One type of alter- 
nating current railway motor, designed for "single-phase" 
operation, is in use on several interurban systems in 
this country, running on high-voltage alternating current 
most of the time, but on continuous current when within 
the city limits. 

357 



ELECTRICITY BOOK FOR BOYS 

Other Forms of Electric Traction 

Electric traction also includes electric automobiles, sup- 
plied by storage-batteries; a slow-speed electric locomotive 
for drawing canal-boats, and called "the electric m.ule"; 
and an ingenious gasolene-electric outfit for driving cars by 
electric motors without any trolley, third rail, or storage- 
battery. The last-mentioned arrangement consists of a set 
of electric car-motors mounted on the trucks in the usual 
way, but supplied with current by a dynamo mounted on the 
car itself and driven by a gasolene-engine. Thus the car 
carries its own power-station about with it, and is indepen- 
dent of any* outside source of electricity. 

The old alchemists sought to transmute matter from one 
form to another; and especially lead and other '' base metals " 
into gold, in order that they might grow rich by concentrat- 
ing the precious metal in their own selfish hands. The 
modern miracle that electricity works for us, the transmu- 
tation of energy, is a higher and broader thing, because it 
multiplies and distributes the world's good things. 



APPENDIX 



A DICTIONARY OF ELECTRICAL TERMS AND PHRASES 

Everybody is interested in electricity, but the ordinary reader, and 
particularly the boy who attempts to use this manual intelligently, will 
come across many technical words and terms that require explanation. 
It would be impossible to incorporate all needful definitions in the text 
proper, and the reader is therefore referred to the technical dictionary on 
the succeeding pages. 

Care has been taken in its compilation to make the definitions com- 
plete, simple, and concise. Some of the more advanced technical terms 
have been purposely omitted as not necessary in a book dealing with 
elementary principles. The student in the higher branches of the science 
will consult, of course, the more advanced text-books. But for our prac- 
tical purposes this elementary dictionary should answer every require- 
ment. To read it over is an education in itself, and the young experi- 
menter in electrical science should always refer to it when he comes 
across a word or phrase that he does not fully understand. 



A. An abbreviation for the word 
anode. 

Absolute. Complete by itself. In 
quantities it refers to fixed units. A 
galvanometer gives absolute readings 
if it is graduated to read direct am- 
peres or volts. An absolute vacuum 
is one in which all residual gases are 
exhausted; an absolute void is the 
theoretical consequent. The absolute 
unit of current is measured in one, 
two, three, or more amperes or volts. 

A-C. An abbreviation expressing 
alternating current. 

Acceleration. The rate of change 
in velocity. 



The increase or decrease of motion 
when acted upon by the electric cur- 
rent. 

Accamtilator. A term applied to 
a secondary battery, commonly call- 
ed a storage-battery. 

Accumulator, Electrostatic. {See 
Electrostatic Accumulator.) 

Accumulator, Storage. A storage- 
battery. 

Acid. A compound of hydrogen 
capable of tmiting with a base to 
form salts. 

Sour, resembling vinegar. 

A sharp, biting fluid. 

Acidometer. A hydrometer used 
to determine the gravity of acids. 
It is employed chiefly in running 



359 



ELECTRICITY BOOK FOR BOYS 



storage-batteries to determine when 
the charge is complete. 

Adapter. A screw - coupHng to 
engage with different size screws 
on either end, and used chiefly to 
connect incandescent lamps to gas- 
fixtures. 

Adherence. The attraction be- 
tween surfaces of iron due to electro- 
magnetic action. The term is used 
in connection with electric brakes — 
electro-magnetic adherence. 

Adjustment. Any change in an 
apparatus rendering it more efficient 
and correct in its work. 

Aerial Condactor. A wire or elec- 
tric conductor carried over house- 
tops or poles, or otherwise suspended 
in the air, as distinguished from un- 
derground or submarine conductors. 

Affinity. The attraction of atoms 
and molecules for each other, due to 
chemical or electrical action. 

Air-condenser. A static condenser 
whose dielectric is air. 

Air-line "Wire. In telegraphy that 
portion of the line-wire w"hich is 
strung on poles and carried through 
the air. 

Alarm, Barglar. A system of cir- 
cuits with an alarm-bell, the wires 
of which extend over a house or 
building, connecting the windows 
and doors with the annunciator. 

Alarm, Electric. An appliance for 
calling attention, generally through 
the ringing of a bell or the operating 
of a horn. 

Alarm, Fire and Heat. An ex- 
pansion apparatus that automati- 
cally closes a circuit and rings a bell. 

Alive, or ** Live.*' _ A term ap- 
plied to a wire or circuit that is 
charged with electricity. A "live" 
wire. 

Active circuits or wires. 

Alloy. Any mixture of two or 
more metals making a scientific com- 
pound. For example: copper and 
zinc to form brass; copper, tin, and 



zinc to form bronze ; copper, nickel, 
and zinc to form German-silver. 

Alternating Current. (See Cur- 
rent, Alternating.) 

Alternating Current-power. Elec- 
trical distribution employing the al- 
ternating current from dynamos or 
converters. 

Alternation. A change in the 
direction of a current; to and fro. 
Alternations may take place with 
a frequency ranging from 500 to 
10,000 or more vibrations per sec- 
ond. 

Alternator. An electric genera- 
tor-dynamo supplying an alternat- 
ing current. 

Amalgam. A combination of mer- 
cury with any other metal. 

Amalgamation. The application 
of mercury to a metal, the surface 
of which has been cleansed with acid. 
Mercury will adhere to all metals, 
except iron and steel, and particu- 
larly to zinc, which is treated with 
mercury to retard the corrosive 
action of acid on its surface. 

Amber. A fossil resin, valuable 
only in frictional electric experi- 
ments. Most of it is gathered on 
the shores of the Baltic Sea between 
Konigsberg and Memel. It is also 
found in small quantities at Gay 
Head, Massachusetts, and in the 
New Jersey green sand. When rub- 
bed with a cloth it becomes excited 
with negative electricity. 

Ammeter. The commercial name 
for an ampere-meter. An instrument 
designed to show, by direct reading, 
the number of amperes of current 
which are passing through a circuit. 

Ampere. The practical unit of 
electric current strength. It is the 
measure of the current produced by 
an electro-motive force of one volt 
through a resistance of one ohm. 

Ampere - currents. The currents 
theoretically assumed to be the cause 
of magnetism. 



360 



APPENDIX 



Ampere - hoan The quantity of 
electricity passed by a current of one 
ampere in one hour. It is used by 
electric light and power companies 
as the unit of energy supplied by 
them , and on which they base their 
reckoning for measuring the charges 
for current consumed. 

Ampere-ring. A conductor form- 
ing a ring or circle. Used in electric 
balances for measuring current. 

Animal Electricity. _ A form of 
electricity of high tension generated 
in certain animal systems — the Tor- 
pedo, Gymnotus, and Celurus. The 
shocks given by these fish, and par- 
ticularly the electric eel, are often 
very severe. 

Annealing. The process of soft- 
ening yellow metals by heating them 
to a cherry redness, then allowing 
them to cool gradually in the air. 

Electric annealing is done by pass- 
ing a current through the body to be 
annealed, and heating it to redness; 
then allowing it to cool gradually. 

Annunciator. An apparatus for 
giving a call from one place to an- 
other, as from a living-room to a 
hotel office, or for designating a 
window or door that may have been 
opened when protected by a bur- 
glar-alarm. 

Annunciator- drop. The little 
shutter which is dropped by some 
forms of annunciators, and whose 
fall discloses a number or letter, 
designating the location from which 
the call was sent. 

Anode. The positive terminal in 
a broken, metallic, or true conduct- 
ing circuit. 

The terminal connected to the car- 
bon-plate of a battery, or to its 
equivalent in any other form of elec- 
tric generator, such as a dynamo or 
a voltaic pile. 

The copper, nickel, gold, or silver 
plates hung in an electro - plating 
bath, and from which the metal is 



supplied to fill the deficiency made 
by the electro - deposition of metal 
on the kathode or negative object 
in the bath. 

Anti-hum. A shackle inserted 
directly in a line-wire near a pole. 
It is provided with a washer or 
cushion of rubber to take up the 
vibrations of a wire. To continue 
the circuit a bridle, or curved piece 
of wire, is connected with the line- 
wires that are attached to the 
shackle. 

Arc. A term applied to an elec- 
tric current flowing from carbon to 
carbon, or from metals separated by 
a short gap, as in the arc street- 
lamps. 

The original arc was produced by 
two vertical rods, through which the 
current passed up and down. When 
not in action the upper ends touched, 
but as the current flowed the ends 
were separated, so that the current, 
passing up one carbon across the 
gap and down the other, formed the 
segment of a circle in jumping from 
one tip to the other. 

An arc of electric flame is of brill- 
iant and dazzling whiteness. The 
voltaic arc is the source of the most 
intense heat and light yet produced 
by man. The light is due principal- 
ly to the incandescence of the ends 
of carbon-pencils, when a current of 
sufficient strength is passing through 
them and jumping over the gap. 
Undoubtedly the transferred carbon 
particles have much to do with its 
formation. The conductivity of the 
intervening air and the intense heat- 
ing to which it is subjected, together 
with its coefficient of resistance, are 
other factors in the brilliant light 
produced. 

Arc-lamp. An electric lamp 
which derives its light from the 
voltaic arc, by means of carbon- 
pencils and a current jumping from 
one to the other. 



36i 



ELECTRICITY BOOK FOR BOYS 



Arc, Quiet* An arc free from the 
hissing sound so common in arc- 
hghts. 

Arc, Simple. A voltaic arc pro- 
duced between only two electrodes. 

Armatwre. A body of iron or other 
material susceptible to magnetiza- 
tion, and which is placed on or near 
the poles of a magnet. 

That part of an electric mechan- 
ism which by magnetism is drawn 
to or repelled from a magnet. 

The core of a dynamo or motor 
which revolves within the field 
magnets, and which is the active 
principle in the generation of cur- 
rent by mechanical means, or in 
the distribution of power through 
electrical influence. Armatures are 
sometimes made of steel, and are 
permanent magnets. These are used 
in magneto-generators, telegraph in- 
struments, and other apparatus. 

Armatare-bar* An armature in a 
dynamo or motor whose winding is 
made up of conductors in the form 
of bars. 

Armatttre-cofl. The insulated 
wire wound around the core of the 
armature of an electric current-gen- 
erator or motor. 

Armatare-core. The central mass 
of iron on which the insulated wire is 
wound ; it is rotated in the field of an 
electric current-generator or motor. 

Armored. Protected by armor; 
as cables may be surrounded by a 
proper sheathing to guard them from 
injury. 

Astatic. Having no magnetic di- 
rective tendency, the latter being a 
general consequent of the earth's 
magnetism. 

Astatic Circuit. (See Circuit, 
Astatic.) 

Astatic Couple. (See Couple, As- 
tatic.) 

Astatic Needle. A combination 
of two magnetic needles so adjusted 
as to have as slight directive tenden- 



cy as possible. The combination is 
generally made up of two needles 
arranged one above the other with 
the poles in opposite directions — 
commonly called "Nobili's Pair." 
These needles require but a slight 
electro-force to turn them one way 
or the other, and are used in astatic 
galvanometers. 

Atmospheric Electricity. {See 
Electricity, Atmospheric.) 

Atom. The ultimate particle or 
division of an elementary substance. 
Electricity is largely responsible for 
the presence of atoms in the atmos- 
phere. 

Atomic Attraction. The attrac- 
tion of atoms for each other. Prin- 
cipally due to electric disturbance. 

Attraction. The tendency to ap- 
proach and adhere or cohere which 
is shown in all forms of matter. It 
includes gravitation, cohesion, adhe- 
sion, chemical affinity, electro-mag- 
netic and dynamic attraction, 

Aurora. A luminous electric dis- 
play seen in the northern heavens. 
It is commonly thought to be the 
electric discharges of the earth into 
the atmosphere, due to revolution of 
the former and to the heat produced 
at the equator. As compared to 
the static machine for generating 
frictional electricity, the earth rep- 
presents the revolving wheel gath- 
ering the current and discharging it 
at the poles. 

Automatic Cut-out. An electro- 
magnetic switch introduced into a 
circuit, so as to break the circuit of 
the latter should it become over- 
loaded with current; it also acts in 
the event of a mechanical interrup- 
tion. 

Automatic Regulation. A speed 
regulator worked by electricity so 
that a uniform flow of current may 
be secured automatically. ■ 

Ayrton's Condenser. This is a 
pile of glass plates separated by 



362 



APPENDIX 



small pieces of glass at the four 
comers, so that the plates cannot 
touch each other. Tin-foil is pasted 
on both sides of every plate, and 
the two coatings are connected. 
The tin-foil on each second plate is 
smaller in area than that on the 
others, and the plates are connected 
in two sets, negative and positive. 
In this construction it will be seen 
that the glass is not the dielectric 
proper, but acts only as the plane 
to which the tin - foil is pasted. 
One set of plates are connected to 
a binding-post" by strips of tin-foil, 
and the other set are connected to 
another binding-post in a similar 
manner. 



B. An abbreviation for Beaume, 
the inventor of the hydrometer scale. 
Thus, in speaking of the gravity of 
fluids, 20° B. means twenty degrees 
Beaume. 

Back Induction. A demagnetiz- 
ing force produced in a dynamo 
when a lead is given to the brushes. 
(See also Induction, Back.) 

Back Shock* A lightning stroke 
received after the main discharge. 
It is caused by a charge induced in 
neighboring surfaces by the main 
discharge. 

Bad Earth. A poor ground con- 
nection, or one having comparatively 
strong electrical resistance. 

Balance. A proper adjustment be- 
tween the apparatus and the electro- 
motive force, thus securing the best 
possible results. 

B. & S. W-G. Abbreviations 
for Brown & Sharp and wire-gauge, 
and referring to the sizes of wire 
and sheet -metal thicknesses that 
are considered standards in Amer- 
ica. 

Bar - armatttre. An armature in 
which the conductors are construct- 
ed of bars. 



Bare-carbons. Electric light car- 
bons whose surfaces are not electro- 
plated with copper. 

Bar -magnet. One whose core 
presents the appearance of a straight 
bar, or rod, without curve or bend. 

Barom,eter. An apparatus for 
measuring the pressure exerted by 
the atmosphere. It consists of a 
glass tube 31 inches long, closed at 
one end, filled with mercury, and 
then inverted, with its open end 
immersed in a cistern of mercury. 
The column of mercury falls to a 
height proportional to the pressure 
of the atmosphere. At the sea- 
level it ranges from 30 to 31 inches. 

Bar-windings. The windings of an 
armature constructed of copper bars. 

Bath. In electro-plating, the so- 
lution or electrolyte used for de- 
positing metal on the object to be 
plated. It may be a solution of cop- 
per, silver, nickel, or other metal. 

In electro - therapeutics it is a 
bath of water with suitable elec- 
trodes and connections for treating 
patients with electricity. 

Bath-stripping. A solution used 
for stripping or removing the metal 
plating from an object. 

Batten. A strip of wood grooved 
longitudinally, in which electric 
light or power wires are set. The 
grooved strip is screwed to the wall, 
the wires being laid in the grooves, 
and then covered with a thin wooden 
strip fastened on with small nails. 

Battery. A combination of parts, 
or elements, for the production of 
electrical action. 

A number of cells connected par- 
allel or in series for the generation 
of electricity. Under this heading 
there are at least one hundred dif- 
ferent kinds. Nowadays the d}'na- 
mo is the cheap and efficient gen- 
erator of electricity. 

Battery Cell, Elements of. The 
plates of zinc and carbon, or of zinc 



3^3 



ELECTRICITY BOOK FOR BOYS 



and copper, in a cell are called ele- 
ments. The plate unattacked by the 
solution, such as the carbon or cop- 
per, is the negative element, while 
the one attacked and corroded by 
the electrolyte is the positive. 

Batteryt Dry, A form of open 
circuit cell in which the electrolyte 
is made practically solid, so that the 
cell may be placed in any position. 
A zinc cup is filled with the electro- 
lyte and a carbon-rod placed in the 
middle, care being taken to avoid 
contact between cup and carbon at 
the bottom of the cell. The gelati- 
nous chemical mass is then packed 
in closely about the carbon, so as to 
nearly fill the cup. A capping of as- 
phaltum, wax, or other non-conduct- 
ing and sealing material is placed 
over the electrolyte, and this hardens 
about the carbon and around the top 
inner edge of the zinc cup. The lat- 
ter becomes the positive pole, the 
carbon the negative. Binding-posts, 
or connections, may be attached to 
the zinc and carbon to facilitate con- 
nections. 

Battery, Galvanic. The old name 
for a voltaic battery. 

Battery, Gravity. A battery in 
which the separation of fluids is ob- 
tained through their difference in 
specific gravity — for example, the 
bluestone cell. The sulphate of cop- 
per solution, being the more dense, 
goes to the bottom, while the zinc 
solution stays at the top. In its ac- 
tion the acid at the top corrodes 
the zinc, while at the bottom the so- 
lution is decomposed and deposits 
metallic copper on the thin copper 
plates. 

Battery, Leclanche. An open cir- 
cuit battery consisting of a jar, a 
porous cup, and the carbon and 
zinc elements, the electrolyte of 
which is a solution of ammonium 
chloride (sal-ammoniac). The car- 
bon plate is placed in the porous cup, 



and packed in with a mixture of 
powdered manganese binoxide and 
graphite, to serve as a depolarizer. 
A half - saturated solution of sal- 
ammoniac is placed in the outer jar, 
and a rod of zinc suspended in it. 
Another form of the battery is to 
omit the porous cup and use twice 
the bulk of carbon, both elements 
being suspended in the one solution 
of sal-ammoniac; this form of bat- 
tery is used for open -circuit work 
only, such as bells, buzzers, and an- 
nunciators. It is not adapted for 
lights, power, or plating purposes. 

Battery Mad. A deposit of mud- 
like character which forms at the 
bottom of gravity batteries, and 
which consists of metallic copper 
precipitated by the zinc. It only 
occurs where wasteful action has 
taken place. 

Battery of Dynamos. A term 
used in speaking of a number of 
dynamos coupled to supply the 
same circuit. They may be coupled 
in series or parallel. 

Battery, Plwnge. A battery in a 
cabinet or frame, so arranged that 
the active plates can be removed 
or raised out of the solutions. This 
is usually accomplished by having 
the plates attached to a movable 
frame which, by means of a ratchet- 
shaft and chains, can be raised or 
lowered. Its object is to prevent 
the corrosion of the plates when not 
in use. 

Battery, Primary. A voltaic cell 
or battery generating electric energy 
by direct consumption of material. 
The ordinary voltaic cell, or gal- 
vanic battery, is a primary battery. 

Battery, Secondary. A storage- 
battery, an accumulator. 

Battery Solution. The active ex- 
citant liquid, or electrolyte, placed 
within a cell to corrode .the posi- 
tive element. Also called Electro- 
poion. 



I 



364 



APPENDIX 



Battery, Storage. A secondary 
battery; an accumulator; a battery 
which accumulates electricity gener- 
ated by primary cells or a dynamo. 

Battery - gauge. A galvanometer 
used for testing batteries and con- 
nections. It is usually small in size, 
and may be carried in a pocket. 

Battery-jar. A glass, earthen, or 
lead vessel which contains the fluids 
and elements of each separate cell 
of a battery. 

Batime Hydrometer. {See Hy- 
drometer, Baume.) 

Becqaerel Ray and Radiation. An 
invisible ray discovered by Becque- 
rel, which is given out by some 
compounds and chemicals — notably 
uranium — and which has the power 
to penetrate many opaque bodies 
and objects impenetrable to the ac- 
tinic rays of ordinary light. These 
rays are used chiefly in connection 
with the photographic dry-plate. 

Bell, Electric. A bell rung by 
electricity. The current excites an 
electro - magnet, attracting or re- 
leasing an armature which is at- 
tached to a vibrating or pivoted 
arm, on the end of which the knock- 
er is fastened. 

Bichromate of Potash. A strong, 
yellowish-red chemical, used chiefly 
in battery fluids and electrolytes. 

Bifilar "Winding. The method 
followed in winding resistance-coils. 
To prevent them from creating flelds 
of force, the wire is doubled and the 
looped end started in the coil. 
Since the current passes in opposite 
senses in the two lays of the wind- 
ing, no field of force is produced. 

Binding. Unattached wire wound 
round armature-coils to hold them ■ 
in place. 

Binding - post. An arrangement 
for receiving the loose ends of wires 
in an electric circuit and securing 
them, by means of screws, so that 
perfect contact will be the result. 



Bi-polar. Possessing two poles. 
Bi - telephone. A pair of tele- 
phones arranged with a curved con- 
necting arm or spring so that they 
can be simultaneously applied to 
both ears. 

Blasting, Electric. The ignition 
of a blasting charge of powder, 
dynamite, or other high explosive 
by an electric spark, or by the heat- 
ing, to red or white heat, of a thin 
wire imbedded in the explosive. 

Block System. A system of sig- 
nalling on railroads. Signal - posts 
are arranged at stated spaces, and 
on these signals appear automatical- 
ly, showing the location of trains to 
the engineers of trains in the rear. 

Blaestone. A trade name for sul- 
phate of copper in a crystallized 
state. 

Bobbin. A spool of wood or oth- 
er non-conducting substance wound 
with insulated wire. In a tangent 
galvanometer the bobbin becomes a 
ring with a channel to receive the 
wire. 

Boiling. In secondary, or stor- 
age, batteries the escaping of hydro- 
gen and oxygen gases, when the bat- 
tery is fully charged, resembles water 
boiling. 

Bonded Rails. Rails used in an 
electric traction system, and which 
are linked or connected together to 
form a perfect circuit. Used prin- 
cipally in the third-rail system. 

Brake, Electro-magnetic. A 
brake to stop the wheels of a mov- 
ing car. It consists of a shoe, or 
ring, which by magnetic force is 
drawn against a rotating wheel to 
stop its revolution. 

Branch. A conductor which leads 
off from a main line to distribute 
current locally. 

Brassing. A process of electro- 
depositing brass in a bath contain- 
ing both copper and zinc. A plate 
of brass is used as an anode. 



ZH 



ELECTRICITY BOOK FOR BOYS 



Brazing, Electric. A process in 
which the spelter is melted, by elec- 
tric current, so that the two parts 
are united as one. 

Break. A point where an elec- 
tric conductor is broken, as by a 
switch or a cut-out. 

Bridge. A special bar of copper 
connecting the dynamos with the 
bus wire in electric lighting- or power 
stations. 

Bronzing. The deposition of 
bronze by electro-plating methods. 
The mixture is of copper and tin, and 
a cast bronze plate is used as an 
anode. 

Brush. A term applied to the 
pieces of copper, carbon, or other 
conducting medium in dynamos and 
motors, that bear against 'the cylin- 
drical surface of the commutators 
to collect or feed in the current. 

Bug. Any fault or trouble in 
the connections or workings of an 
electrical apparatus. The term orig- 
inated in quadruplex telegraphy, 
and probably had some connection 
with the Edison bug-killer that he 
invented when a boy. 

Buoy, Electric. A buoy to in- 
dicate dangerous channels in har- 
bors and to mark wrecks and reefs. 
It is provided with an electric light 
at night, and with a gong or an elec- 
tric horn by day. 

Burner, Electric. A gas-burner 
so arranged that the flame may be 
lighted by electricity operated by 
a push-button at some distance from 
the fixture, or, close at hand, by 
means of a chain or pull-string. 

Burning. In a dynamo, the im- 
proper contact of brushes and com- 
mutator, whereby a spark is pro- 
duced and an arc formed which 
generates heat and causes the metal 
parts to bum. 

Bus -rod. A copper conductor 
used in power-plants to receive the 
current from the battery of dynamos. 



The distributing leads are connected 
to these rods. 

Butt - joint. A joint made by 
bringing the ends of wires together 
so that the ends butt. They are 
then soldered or brazed. 

Button, Electric. A form of 
switch that is operated by pushing 
a button mounted on a suitable 
base. Used principally for ringing 
bells, operating lights, etc. 

Buzzer. An electric alarm, or 
call, produced by the rapid vibra- 
tion of an armature acted upon by 
electro-magnetism. The sound is 
magnified by enclosing the mechan- 
ism in a resonant box. 

An apparatus resembling an elec- 
tric bell minus the bell and clapper. 
The buzzer is used in places where 
the loud ring of a bell would be a 
nuisance. 



C. An abbreviation for centi- 
grade when speaking of thermal 
temperature. In chemistry the 
centigrade scale is used extensively, 
but in air temperatures the Fahren- 
heit scale is universally employed. 

Cable, Aerial. A cable that con- 
tains a number of wires separ.viely 
insulated, the entire mass being pro- 
tected by an external insulation. 
It is suspended in the air from pole 
to pole, and sometimes its weight 
is so great that a supporting wire is 
carried along with it (usually over- 
head), the large cable being sus- 
pended from it by cable-hangers. 

Cable Box. A box to receive cable 
ends and protect them; also, the box 
in which cable ends and line-wires are 
joined. Submarine cable boxes are 
usually near the ground, while tele- 
phone and telegraph cable boxes are 
mounted on poles, the cables run- 
ning from the ground and up the 
poles to the boxes. 

Cable-core. The conductors of a 



366 



APPENDIX 



cable which make up its interior 
mass. For the convenience of hne- 
men the wires are often insulated 
with different-colored materials so 
that testing is not necessary when 
making connections. 

Cable - hanger. A metallic grip, 
usually of sheet metal, arranged to 
clasp two or more wires. It is fas- 
tened to the supporting wire by a 
hook and eye, or by small bolts with 
thumb-nuts. 

Cable-head. A rectangular board 
equipped with binding-posts and 
fuse wires so that the connections 
may be made between the cable ends 
and the overhead or line-wires of a 
system. 

Cables. An insulated electric 
conductor of large diameter, often 
protected by armor or metallic 
sheathing, and generally containing, 
or made up, of several separately 
insulated wires. Cables supply cur- 
rent to tractio"n lines ; power, through 
subterranean passages; communica- 
tion, by submarine connection; and 
light, by overhead or underground 
conduits. 

Call-bell. A bell that is rung by 
pressing a button, and which is 
operated by electricity. 

Calling - drop. A drop - shutter 
which is worked by electricity in a 
telegraph or telephone exchange; it 
denotes the location from which the 
call was sent in. Small red incan- 
descent lamps have taken the place 
of the drops in most of the large tele- 
phone exchanges, for they are noise- 
less and do not annoy the operators 
as the drops and buzzers did. 

Candle - power. The amount of 
light given by the standard candle. 
The legal English and American 
standard is a sperm candle burning 
two grains a minute. 

Candle, Standard. The standard 
of illuminating power; a flame 
which consumes two grains of sperm 



wax per minute, and produces a light 
of a brightness equal to one candle- 
power. 

Caotitchouc. India - rubber. So 
named because originally its chief 
use was to erase or rub off pencil 
marks. It is a substance existing, 
in a thick fluid state, in the sap or 
juices of certain tropical trees and 
vines; it possesses a very high value 
as an insulator for wire and circuits. 
The unworked, crude rubber is called 
virgin gum, but after it is kneaded 
it is called masticated or pure gum 
rubber. 

Capacity. A term used when 
speaking of the carrying power of a 
wire or circuit. The capacity of a 
wire, rod, bar, or other conductor 
is sufficient so long as the current 
does not heat it. Directly electric 
heat is generated, we speak of the 
conductor as being overloaded or 
having its capacity overtaxed. 

Capacity of a Telegraph Con- 
dtictor. The electric capacity may 
be identical in quality with that of 
any other conductor. In quantity 
it varies not only in different wires, 
but for the same wire under different 
conditions. A wire reacting through 
the surrounding air, or other di- 
electric, upon the earth represents 
one element of a condenser, the 
earth in general representing the 
other. A wire placed near the 
earth has greater capacity than one 
strung upon high poles, although 
the wires may be of identical length 
and size and of the same metal. 
The effect of high capacity is to re- 
tard the transmission of current, 
the low capacity facilitates trans- 
mission. 

Capacity, Storage. In secondary 
batteries, the quantity of electric 
current they can supply, when fully 
charged, without exhaustion. This 
capacity is measured or reckoned in 
ampere-hours. 



?>^1 



ELECTRICITY BOOK FOR BOYS 



Carbon, One of the elements in 
graphitic form used as an electric- 
current conductor. It is the only 
substance which conducts electricity, 
and which cannot be melted with 
comparative ease by increase of 
current. It exists in three modi- 
fications — charcoal, graphite, and the 
diamond. In its graphitic form it 
is used as an electro-current con- 
ductor, as in batteries and arc-light 
electrodes, and as filaments in in- 
candescent lamps. In arc-lamp use 
the carbons are usually electro- 
plated on the outside with a film of 
copper which acts as a better con- 
ductor. 

Carbon, Artificial. Carbon-dust, 
powdered coke, or gas carbon is 
mixed with molasses, coal-tar, syrup, 
or some similiar carbonaceous fluid, 
so that the mass is plastic. It can 
then be moulded or pressed into 
shapes, and heated to full redness for 
several hours by artificial or electric 
heat. For lamp-carbons the mixt- 
ure is forced through a round die 
by heavy pressure, and is cut into 
suitable lengths, then fired or baked. 

After removing and cooling, the 
carbons are sometimes dipped again 
into the fluid used for cementing the 
original mass and re-ignited. This 
process is termed "nourishing." All 
carbon is a resisting medium, but at 
high temperature the resistance is 
only about one-third as great; that 
is, the current will pass through a 
red-hot carbon three times better 
than through the cold carbon; or a 
current of thirty amperes will be con- 
ducted as easily through a hot carbon 
as ten amperes through a cold one. 

Carbon-cored. A carbon for arc- 
lamps, the core being of softer car- 
bon than the outer surface. It is 
supposed to give a steadier light, 
and fixes the position of the arc. 

Carbon-dioxide. A compound gas, 
or carbonic-acid gas. It is a dielectric. 



Carbon - holders. In arc - lamps, 
the clamps arranged to hold the car- 
bon-pencils. 

Carbonization. The ignition of 
an organic substance in a closed ves- 
sel, so as to expel all constituents 
from it except the carbon. 

A destructive distillation. 

Carbon Resistance. {See Resist- 
ance, Carbon.) 

Carbon Volatilization. In arc- 
lamps the heat is so intense that it 
is believed a part of the carbon- 
pencil is volatilized, as vapor, be- 
fore being burned or oxidized by the 
oxygen of the air. 

Carbons, Bare. {See Bare Car- 
bons.) 

Carrying Capacity. In a current- 
conductor, its carrying capacity up 
to the heating-point. It is expressed 
in amperes. 

Cascade. The arrangement of a 
seiies of Leyden-jars in properly 
insulated stools, or supports, for 
accumulating frictional electricity. 
They are arranged in a manner some- 
what similar to a battery of galvanic 
cells, the inner coating of one being 
connected to the outer coating of 
the next, and so on through the 
series. 

Case-hardening, Electric. A proc- 
ess by which the surface of iron is 
converted into steel by applying a 
proper carbonaceous material to it 
while it is being heated by an elec- 
tric current. 

Cautery, Electric. An electro- 
surgical appliance for removing dis- 
eased parts or arresting hemor- 
rhages. It takes the place of the 
knife or other cutting instrument. 
It is a loop of platinum wire heated 
to whiteness by an electric current. 

C.C. An abbreviation common- 
ly used for cubic-centimeter. It is 
usually written in small letters, as 50 
C.C, meaning 50 cubic-centimeters. 

Cell, Electrolytic. A vessel con- 



368 



APPENDIX 



taining the electrolyte used for elec- 
tro-plating. 

Cell, Regenerated* A cell restored 
to its proper functions by a process 
of recharging. 

Cell, Standard. Meaning the same 
as battery. The vessel, including 
its contents, in which electricity is 
generated. 

Cell, Storage. Two plates of 
metal, or compounds of metal, whose 
chemical relations are changed by 
the passage of an electric current 
from one plate to the other through 
an electrolyte in which they are im- 
mersed. 

Cements, Electrical. Cements of 
a non - conducting nature, such as 
marine glue and sticky compounds, 
used in electrical work. 

Centrifugal Force. A diametric 
revolving force which throws a 
body away from its axis of rotation. 
A merry-go-round is a simple ex- 
ample of this force. The more 
rapidly the platform revolves the 
greater the tendency for those on 
it to be thrown off and out from the 
centre. The high velocity attained 
by the armatures in motors and 
dynamos would throw the wires out 
of place and cause them to rub 
against the surfaces of the field- 
magnets. Consequently, wire bands 
or binders are necessary to keep the 
coils of wire from spreading under 
the influence of the centrifugal force. 

Charge. The quantity of elec- 
tricity that is present on the surface 
of a body or conductor. 

The component chemical parts 
that are employed to excite the ele- 
ments of a cell in generating electric 
current. 

Charge, Residual. After a Ley- 
den-jar, or other condenser, has been 
discharged by the ordinary meth- 
ods, a second discharge (of less 
amount) can be had after a few 
minutes' v/aiting. This is due to 



what is known as the residual 
charge, and is connected in some 
way with the molecular distortion 
of the dielectric. 

Chemical Change. When bodies 
unite so as to satisfy affinity, or to 
bring about the freeing of thermal or 
other energy, the union is usually 
accompanied by sensible heat or 
light. Sulphuric acid added to wa- 
ter produces heat ; a match in burn- 
ing produces light. Another form 
of chemical change is decomposition 
or separation (the reverse of com- 
bination), such as takes place in the 
voltaic -battery, the electro - plating 
bath, and other forms of electrolysis. 
This is not accon-.panied by heat 
or light, but by the evolution of elec- 
tricity. 

Chemical Element. {See Ele- 
ment, Chemical.) 

Chemistry. The science which 
treats of the atomic and molecular 
relations of the elements and their 
chemical compounds. Chemistry is 
divided into many departments, but 
electro-chemistry treats only of the 
science wherein electricity plays an 
active part, such as batteries, elec- 
tro-plating, and electro-metallurgy. 

Choking-coil. (See Coil, Choking.) 

Circle, Magic. A form of elec- 
tro-magnet. It is a thick circle of 
round iron used in connection with 
a magnetized coil to illustrate elec- 
tro-magnetic attraction. 

Circuit. A conducting - path for 
electric currents. Properly speak- 
ing, a complete circuit has the ends 
joined, and includes a source of cur- 
rent, an apparatus, and other ele- 
ments introduced in the path. When 
the circuit is complete it is called 
active. The term circuit is also 
applied to portions of a true circuit 
— as, an internal or external circuit. 

Circuit, Astatic. A circuit so 
wound, with reference to the direc- 
tion of the currents passing through 



369 



ELECTRICITY BOOK FOR BOYS 



it, that the terrestrial or other lines 
of force have no directive effect 
upon it. 

Circuit - breaker. Any apparatus 
for opening and closing a circuit, 
such as switches, automatic cut-outs, 
lightning-arresters, and the like. 

A ratchet-wheel engaged with a 
spring, or wire, which rests against 
the teeth. The current passes 
through the wire, the wheel, and 
axle. The wheel is revolved by a 
crank, and -as the ratchets pass the 
spring, or wire, an instantaneous 
make-and-break occurs. The speed 
of the wheel regulates the frequency 
of the interruptions. 

Circwitt External. A portion of 
the circuit not included within the 
generator, such as a secondary tele- 
graph key and sounder. 

Circuit, Grotinded. A circuit in 
which the ground is used as a con- 
ductor. This is common in tele- 
graph and telephone lines, partic- 
ularly for short distances where the 
conductivity of the earth does not 
offer too much resistance. 

Circtiit, Incandescent. A circuit 
in which incandescent lamps are in- 
stalled. 

Circuit Indicator. A pocket-com- 
pass, galvanometer, or other device 
for indicating or detecting the con- 
dition of a wire, whether it is active 
or dead, and, if active, in which di- 
rection the current is flowing. It 
may also give a general idea of its 
strength. 

Circuit, Internal. That portion 
of an electric circuit which is in- 
cluded within the generator. 

Circuit Loop. A minor circuit in- 
troduced, in series, into another cir- 
cuit by a switch or cut-out, so that it 
becomes a part of the main circuit. 

Circuit, Main. A circuit, or main 
line, includes the apparatus supply- 
ing current to it. Thus distinguished 
from a local circuit. 



Circuit, Metallic. A circuit in 
which the current outside the gen- 
erator passes through metal parts 
or wire, but not through the ground. 
Electric light and power lines are 
always metallic circuits. An elec- 
tro-plating apparatus may be prop- 
erly termed a metallic circuit, al- 
though a part of the circuit is formed 
by the electrolyte in the bath. The 
essential meaning of the words metal- 
lic circuit is that the earth does not 
form a part of the return circuit. 

Circuit, Open. A circuit in which 
a switch has been opened to pre- 
vent the continuous flow of current, 
such as an electric-bell circuit, which 
normally remains open, and which 
is active only when the push-button 
is pressed, thereby closing the circuit 
and operating the bell. An open- 
circuit battery is one that remains 
inactive when the circuit is open. 

Circuit, Parallel. A term signi- 
fying a multiple circuit. 

Circuit, Quadruple. A single cir- 
cuit capable of having four messages 
transmitted over it simultaneously — 
two in one direction, and two in the 
other. 

Circuit, Return. In telegraphy 
the ground is used as the return cir- 
cuit. It is also that portion of a^ 
circuit which leads from an appara- 
tus back to the terminal of a dyna- 
mo or battery, usually the negative 
wire. 

Circuit, Short. A connection be- 
tween two parts of a circuit, causing 
the current to skip a great part of 
its appointed path. Short-circuits 
prevent the proper working of any 
electrical apparatus. 

Circuit, Simple. A circuit con- 
taining a single generator, the prop- 
er wire for carrying the current, and 
a switch to operate it. An electric- 
bell line, a single telegraph line, or 
a direct telephone line are all sim- 
ple circuits. 



^1^ 



APPENDIX 



Clamp. A tool for grasping and 
holding the ends of wires while join- 
ing them. 

The appliance for holding the car- 
bon-pencils in arc-lamps. 

Qeats. Blocks of wood, porce- 
lain, or other insulating material 
used to hold wires against a wall or 
beam. They have one, two, and 
three notches at one side, for single, 
double, and three wire systems. 

Q«tch, Electric. A form of mag- 
netic brake applied to car -wheels, 
the armatures of motors, and other 
revolving mechanism, whereby the 
current, passing through a coil, 
magnetizes a mass of cast-iron, and 
brings it to bear frictionally upon 
the moving parts of the mechanism. 

Code, Gpher. A set of discon- 
nected words which, in accordance 
with a prearranged key, stand for 
whole sentences and phrases. Com- 
mercially the system is used as a 
short-cut — ten words perhaps mean- 
ing what otherwise it would take 
forty or fifty words to express. It is 
used extensively in telegraphy, both 
as an abbreviated message and as a 
means for securing secrecy. 

Coherer. Conducting particles 
constituting a semi-conducting 
bridge between two electrodes, and 
serving to detect electro-magnetic 
waves. The coherer in wireless 
telegraphy is understood to mean 
that form of radio-receiver which, 
being normally at high resistance, is, 
under the influence of Hertzian- 
waves, changed to a low resistance, 
thus becoming relatively a con- 
ductor. Tubes of various kinds 
have been used for this purpose. 
Within them is a filling of carbon 
granules, copper filings, nickel and 
silver filings, and other substances. 
Marconi's coherer consists of a tube 
one and one-half inches long and 
one-twelfth inch internal diameter. 
This is filled with filings — 90 per 



cent, of nickel, 10 per cent, of silver. 
A globule of mercury coats the out- 
er surface of each grain with a thin 
film of the quicksilver. Into both 
ends a piece of pure silver wire is 
plugged. These latter are a quar- 
ter of an inch long, and fit the tube 
very accurately. The tube is thus 
sealed, and it is considered prefer- 
able to have a slight vacuum with- 
in it. 

Coil. A strand of wire wound in 
circular form about a spool, a soft- 
iron core, or in layers, as a coil of 
rope. 

An electro-magnetic generator. 

A helix. {See also Induction, Re- 
sistance, Magnetizing.) 

Coil, Choking. A form of resist- 
ance to regulate the flow of current. 
Any coil of insulated wire wound 
upon a laminated or divided iron 
core forms a choking-coil. In alter- 
nating-current work special choking- 
coils are used. They have a mov- 
able iron core, and by thrusting it 
in or out the power is increased or 
diminished, thus raising or lowering 
the lights, the same as gas is regu- 
lated. 

Coil, Faradic. The name given 
to a medical induction-coil or faradic 
machine. 

Coil, Induction. A coil in which 
the electro-motive force of a portion 
of a circuit is, by induction, made 
to produce higher or lower electro- 
motive forces in an adjacent circuit, 
or in a circuit a part of which ad- 
joins the original circuit. There 
are three principal parts to all in- 
duction - coils — the core, the pri- 
mary coil, and the secondary coil. 
The core is a mass of soft iron, cast 
or wrought, but preferably divided 
— for example, a bundle of rods or 
bars. The primary coil of com^ 
paratively larger wire is wound 
about this core, each layer being 
properly insulated and varnished, or 



371 



ELECTRICITY BOOK FOR BOYS 



coated with melted paraffine, to 
bind the wires. The secondary coil 
is of fine wire, and is wound about 
the primary coil. A great many 
turns of the fine wire are necessary, 
and care must be taken to properly 
insulate each layer and shellac the 
wires. The primary must be well 
insulated from the secondary coil, 
so as to prevent sparking, which 
would destroy the insulation. A 
make-and-break is operated by the 
primary coil, and is constructed 
upon the general form of an electric 
bell or buzzer movement. Extra 
currents which interfere with the 
action of an induction-coil are 
avoided by the use of a condenser. 
(See also Condenser.) The induction- 
coil produces a rapid succession of 
sparks which may spring across a 
gap of thirty or forty inches, accord- 
ing to the size of the coil. Induction- 
coils are used extensively in electric 
work, especially in telephone trans- 
mitters, wireless telegraphy, electric 
welding, and in the alternating-cur- 
rent system. 

Coil, Magnetizing. A coil of in- 
sulated wire so wound that a well 
or aperture will be formed. Within 
this well a piece of steel is placed, so 
that an electric current, passing 
through the wires, will magnetize the 
steel; or a steel rod mcey be passed 
in and out of the hole several times 
while a strong current is travelling 
through the coil, thus magnetizing 
the rod. 

Coil, Resistance. A coil so con- 
structed that it will offer resistance 
to a steady current of too great 
electro-motive force for the safety 
of the apparatus. Generally the 
coil is made by doubling the wire 
without breaking it, then starting 
at the doubled end to wind it in 
coil or spring fashion. If the wire 
is too heavy to wind double, a single 
strand is wound on a square or tri- 



angular insulator in which notches 
are made. Then, alternately be- 
tween the coils, the second strand 
is wound. The strands are joined 
at one end of the coil, but those at 
the other are left free for unions with 
other wires. (See also Resistance.) 

Coil, Retarding. A choking-coil. 
A resistance-coil. 

Coil Ribbon. Instead of wire, 
flat, thin strips of sheet-metal are 
sometimes used for resistance-coils, 
doubled, as explained above. The 
wraps are insulated with sheet-mica, 
micanite, or asbestos, to prevent 
short-circuiting. 

Coil, Rtihmkoff. A common type 
of induction-coil with a vibrator or 
circuit - breaker. Used with con- 
stant and direct current. 

A step-up transformer with a cir- 
cuit-breaker attachment. 

Coils, Idle. Coils in a dynamo 
in which no electro-motive force is 
being generated or developed. 

Coils that, through broken connec- 
tions or short circuits, are inactive. 

Column, Electric. An old name 
for the voltaic pile. The apparatus 
made up of a pile of disks of copper 
and zinc, separated by pieces of flan- 
nel wet with acidulated water. 

Comb. A bar from, which a num- 
ber of teeth project like the teeth 
of a comb. It is used as a collector 
of electricity from the plate of a 
frictional electric machine. 

Commutator. An apparatus used 
on motors and dynamos and in- 
duction - coils for changing the di- 
rection of currents. It is made in 
a variety of types, but usually in 
the shape of insulated bars closely 
packed about an armature shaft. 

Commotator-bars. The metallic 
segments of a dynamo or motor- 
commutator. 

Commutators, Qaiet. Commuta- 
tors that do not spark during the 
revolutions of the armature. 



372 



APPENDIX 



Compass. An apparatus for in- 
dicating the directive force of the 
earth upon the magnetic needle. 
It consists of a case covered with 
glass, in which a magnetized needle, 
normally pointing to the north, is 
balanced on a point at the centre. 
Under the needle a card is arranged 
on which the degrees or points of the 
compass are inscribed. A valuable 
instrument in electrical work, mag- 
netism, etc. 

Compass, Liquid. A form of 
marine compass. The needle is at- 
tached to a card or disk which floats 
in alcohol or other spirits, so as to 
check undue oscillation. 

Compass, Mariners*. A compass 
in which the needle is attached to a 
card that rotates in pointing to the 
north. A mark, called the "lub- 
ber's mark," is made upon the case, 
and this is in line with the ship's 
keel, so that a glance at the card 
will indicate the direction in which 
the ship is headed. 

Compass, Spirit. A form of mar- 
iners' compass in which the bowl, 
or case, is sealed and filled with 
alcohol. The compass-card works 
as a spindle, and, by a series of 
air compartments, floats on the alco- 
hol. The friction of the pivot is 
thereby greatly diminished, mak- 
ing the compass a very sensitive 
one. 

Compass, Standard. A compass 
employed as a standard by which 
to compare other compasses. 

Condenser. An appliance for 
storing up electro-static charges; it 
is also called a static accumulator. 
The telegraphic condenser consists 
of a box packed full of sheets of tin- 
foil having a sheet of paraffined pa- 
per or sheet-mica between every 
two sheets. The alternate sheets of 
tin-foil are connected together, and 
each set has its binding-post. {See 
also Electrostatic Accumulator.) 



Condenser, Air. (See Air-conden- 
ser.) 

Condenser, Ayrton*s. (See Ayr- 
ton's Condenser.) 

Condenser-plate. {See Plate, Con- 
denser.) 

Condenser, Sliding. An appara- 
tus in the form of a Leyden-jar 
whose coatings can be slid past each 
other to diminish or increase the 
face area , and also to diminish or in- 
crease the capacity of the condenser. 

Conductance. The conducting 
power of a mass of material, vary- 
ing according to its shape and di- 
mensions. The cylindrical or round 
conductor is the best type for the 
conveyance of electric currents. 

Conduction. The transmission of 
electricity through an immobile me- 
dium, such as a wire, or rod, or a bar. 

Conductivity. Ability to conduct 
electric currents. The conductivity 
of a wire is its power to conduct or 
transmit a current. Glass has no 
conductivity, and it is therefore a 
non-conductor. 

Conductivity, Variable. The 
change in the conducting or trans- 
mitting powers of metals and sub- 
stances under different tempera- 
tures. Hot metal conducts an elec- 
tric current better than coid. A 
hot carbon-pencil in an arc-light 
conducts the current better than 
when the light is first started, for 
as it warms up under the influence 
of the arc-flame the current passes 
more freely. Five minutes after the 
current is turned on the lamps in the 
circuit give a steady light, and do 
not sputter as when they first start 
up. 

Conductor. Anything which per- 
mits the passage of electric current. 
The term conductor is a relative one, 
and, excepting a vacuum, there is 
probably no substance that has not 
some conductive power. Metals, 
beginning with silver, are the best 



373 



ELECTRICITY BOOK FOR BOYS 



conductors, liquids next, glass the 
worst. The ether, or air, is a con- 
ductor of sound and electric vi- 
bratory disturbances, but not in 
the same sense as the ground. The 
air conducts frictional electricity, 
while the ground acts as a conductor 
for the galvanic current, or "cur- 
rent electricity." By this last term 
is meant electricity which flows con- 
tinually, instead of discharging all 
at once, with an accompanying 
spark or flash. 

Conductor, Overhead. Overhead 
electric lines, wires or cables, for 
conducting current. Geneirally poles 
are erected for this purpose. 

Condtictor, Prime. A cylindrical 
or spherical body with no points or 
angles, but rounded everyw^here 
and generally of metal. If made of 
other material, such as wood, glass, 
or composition, its entire surface is 
rendered conductive by being cov- 
ered with sheet-metal, such as tin- 
foil, gold-leaf or tinsel, applied to it 
with paste, shellac, or glue. A 
prime conductor should be mounted 
on an insulated stand ; it is employed 
to collect and retain frictional elec- 
tricity generated by a static ma- 
chine. 

Condtictor, Undergrotind. An in- 
sulated conductor which is placed 
under the surface of the earth, 
passing through conduits. 

Connect. The act of bringing two 
ends of wire together, either tem- 
porarily or permanently. Bringing 
one end of a conductor into contact 
with another so as to establish an 
electric connection. 

Connector. A sleeve, with screws 
or other clamping device, into which 
the ends of wires or rods may be 
passed and held securely. A bind- 
ing-post and spring-jack comes un- 
der this head. 

Contact. The electrical union of 
two conductors, whether temporary 



or permanent. It may be establish- 
ed by touching the ends or terminals 
of a circuit through the agency of a 
push-button, a telegraph-key, an 
electric switch, etc. 

Contact - breaker. (The same as 
Circuit-breaker, which see.) 

Contact, Loose. A contact form- 
ed by two or several surfaces im- 
posed one upon another and held by 
their weight alone. 

Contact-point. A point, or stud, 
often of silver or platinum, arranged 
to come into touch with a contact- 
spring, such as the vibrating arma- 
ture of an electric bell. 

Contact - spring. A spring con- 
nected at one end of a lead and ar- 
ranged to press against another 
spring or plate, so that a plug may be 
inserted between the contact-points. 

Controller. The lever or handle 
on the switch-board of a resistance- 
coil, by means of which electric cur- 
rent is let in or kept out of a circuit. 

Controlling Force. In galvanom- 
eters and similar instruments, the 
force used to bring the needle or in- 
dicator back to zero. 

Converter. An induction-coil used 
with the alternating current for 
changing the potential difference 
and inverting the available current. 
High alternating voltage may be 
converted into lower direct-current 
voltage, thereby increasing the am- 
perage or current. A converter con- 
sists of a core of thin iron sheets, 
wound with a primary coil of fine 
insulated wire, with many convolu- 
tions or turns. Also, a secondary 
coil made up of coarse insulated 
wire with fewer convolutions. The 
coil may be jacketed with iron to 
increase the permanence. 

Converter, Rotary. A combined 
motor and dynamo whose function 
is to transform a current of high or 
low voltage (A-C, or D-C.) into any 
other kind of current desired. 



374 



APPENDIX 



Convolution. The state of being 
convolved; a turn, wrap, fold, or 
whorl. A clock-spring is a familiar 
example. 

Copper-bath. A solution of sul- 
phate of copper used in electro- 
plating, electrotyping, and copper- 
refining by electricity. 

Cord, Flexible. A flexible - wire 
conductor made up of ma,ny strands 
of fine wire and properly insulated 
so that it may be easily twisted, bent, 
or wrapped. Flexible wire is used as 
the conductors for portable electric 
lights, push-buttons, medical coils, 
etc. 

Core. The iron mass (generally 
located in the centre of a coil or 
helix) which becomes highly mag- 
netic when a current is flowing 
around it, but which looses its mag- 
netism immediately that the current 
ceases to flow. 

A conductor or the conductors of 
an electric cable made up of a sin- 
gle strand or many strands laid to- 
gether and twisted. These may be 
of bare metal, or each one insulated 
from the others. 

Core -disks. Disks of thin wire, 
for building up armature -cores. 
The usual form of a core is round or 
cylindrical. A number of thin disks, 
or laminations, of iron strung upon 
the central shaft, and pressed firm- 
ly together by the end-nuts or keys. 
This arrangement gives a cylinder as 
a base on which to wind the in- 
sulated wire that forms a part of the 
armature. 

Core -disks. Pierced. Core -disks 
for an armature of a motor or dyna- 
mo, which have been pierced or 
bored out around the periphery. 
Tubes of. insulating material, such 
as fibre, rubber, or paraffined paper, 
are inserted in the holes and through 
these the windings of wire are car- 
ried. The coils are thus imbedded 
in the solid mass of iron, and are 



protected from eddy currents; also 
they act to reduce the reluctance of 
the air-gaps. This arrangement is 
very good, from a mechanical point 
of view, but in practice its use is 
confined to small motors only, and 
dynamos generating under one hun- 
dred volts. 

Core - disks, Toothed. Core - disks 
of an armature or motor where 
notches are cut from the periphery. 
When they are locked together, to 
form the armature-core, the coils of 
wire lie in the grooves formed by a 
number of the disks bound together. 
This construction reduces the act- 
ual air - gaps and keeps the coils 
equally spaced. 

Core, Laminated. The core of an 
armature, an induction-coil, a con- 
verter, or any similar piece of ap- 
paratus, which is made up of plates 
or disks, insulated more or less per- 
fectly from one another by means of 
mica or paraffined paper. The ob- 
ject of laminations is to prevent the 
formation of Foucault currents. A 
core built up of disks is sometimes 
called a radially laminated core. 

Core, Ring. A dynamo or motor 
armature-core which forms a com- 
plete ring. 

Core, Stranded. The core of a 
cable, or a conducting core made up 
of a number of separate wires or 
strands laid or twisted together. 

Core, Tubular. Tubes used as 
cores for electro-magnets, and also 
to produce small magnetizing power. 
Tubular cores are nearly as efficient 
as solid ones in straight magnets, 
because the principal reluctance is 
due to the air-path. On increasing 
the current, however, the tubular 
core becomes less efficient. 

Coulomb. The practical unit of 
electrical quantity. It is the quan- 
tity passed by a current of one am- 
pere intensity in one second. 

Couple. The combination of two 



375 



ELECTRICITY BOOK FOR BOYS 



electrodes and a liquid, the elec- 
trodes being immersed in the latter, 
and being acted on differentially by 
the liquid. This combination con- 
stitutes a source of electro-motive 
force, and, consequently of current, 
and is called the galvanic or voltaic 
cell or battery. 

Couple, Astatic. A term some- 
times applied to astatic needles when 
working in pairs. 

Coupling. The union of cells or 
generators constituting a battery; 
the volume of current, or electro- 
motive force, is thereby increased. 

C. P. An abbreviation for "can- 
dle power ' ' ; also meaning ' ' chemi- 
cally pure, ' ' when speaking of chemi- 
cals. 

G*ater. The depression that forms 
in the positive carbon of a voltaic- 
arc. 

Creeping. A phenomena met with 
in solution batteries. The electro- 
lyte creeps up the sides of the con- 
taining jar and evaporates, leaving 
a deposit of salts. Still more solu- 
tion creeps up through the salts until 
it gets clear to the top and runs over. 
To prevent this the tops of the jars 
should be brushed with hot paraffine 
for a distance of two inches from 
the upper edge. The salts will not 
form on paraffine. Oil is sometimes 
poured on the top of the battery 
solution, but this affects the ele- 
ments if it touches them, and makes 
their surfaces non-conducting. 

Crucible, Electric. A crucible for 
melting refractory substances, or for 
reducing ores by means of the elec- 
tric arc produced within it. Prob- 
ably the result obtained is due more 
to current incandescence than to the 
action of the arc. 

Crystallization, Electric. Under 
proper conditions many substances 
and liquids take a crystalline form. 
When such action is brotight about 
by means of electricity the term 



electric crystallization may be ap- 
plied to the phenomenon. A solu- 
tion of nitrate of silver, when de- 
composed by a current, will give 
crystals of metallic silver. A solu- 
tion of common salt or brine, when 
electrically decomposed, will pro- 
duce sodium and chlorine. The 
sodium appears at the leading - out 
electrode and readily unites with 
carbonic-acid gas, which is injected 
into the apparatus. The result of 
the combination is carbonate of soda, 
one of the most important products 
of the alkali industry. 

Current, Alternating. A current 
flowing alternately in opposite di- 
rections. It is a succession of cur- 
rents, each of short duration and of 
direction opposite to that of its pred- 
ecessor. Abbreviation, A-C. 

Current, Amperage. The volume 
of electricity passing through any 
circuit per second, the flow being 
uniform. 

Current, Constant. An unvary- 
ing current. A constant - current 
system is one in which the current 
is uniformly maintained — for ex- 
ample, in electric light, power, and 
heat plants. 

Current, Continuous. A current 
of one direction only, or the reverse 
of an alternating current. 

Current, Direct. A current of un- 
varying direction, as distinguished 
from the alternating. Abbreviation, 
D-C. 

Current Distribution, Uniform. 
A steady current; a current whose 
density in a conductor is always the 
same at all points. 

Current, Induced. A current 
caused by electro-dynamic induction. 

Current, Low Potential. A cur- 
rent of low pressure. 

A term applied to lov/ electro- 
motive force. 

Current, Make-and-break. A cur- 
rent which is continually broken or 



376 



APPENDIX 



intemipted and started again. The 
term is applied only where the in- 
terruptions occur in rapid succes- 
sion, as in the action of an induc- 
tion-coil or pole-changer. 

The alternating current. 

Cwrrent-meter. An apparatus for 
indicating the strength of a current, 
such as an ammeter. 

Carrentt Oscillating. A current 
periodically alternating. 

Ctjrrent, Periodic. A current with 
periodically varying strength or di- 
rection. A current alternating peri- 
odically. 

Current, Polarizing. A current 
which causes polarization. 

Current - reverser. A switch or 
other contrivance for reversing the 
direction of a current in a conductor. 

Current, Undulating. A current 
whose direction is constant but 
whose strength is continuously vary- 
ing. 

Currents, Eddy. Useless currents 
in an armature, in the pole pieces, 
and in the magnetic cores of dyna- 
mos and motors. They are created 
by the high speed of the armature 
in its rotation, or by other electric 
currents induced by the armature's 
motion through magnetic fields. 

Currents, Faradic. Induced cur- 
rents. They take their name from 
Michael Faraday, the original in- 
vestigator of the phenomena of 
electro - magnetic induction. The 
secondary or induced electro-mag- 
netic currents and their accompany- 
ing phenomena. 

A series of alternating electro- 
static discharges from influence 
machine, such as the Holtz and 
Wimshurst. 

The simple and commonly under- 
stood Faradic currents are those 
produced in the medical battery, 
and used in medical therapeutics. 

Currents, Foucault. A form of 
currents produced in revolving ar- 



mature-cores ; sometimes called eddy 
currents. They are useless. 

Currents, Harmonic. Currents 
which alternate periodically, and 
vary harmonically. Currents which 
vibrate at certain pitches, as, for 
instance, the currents in wireless 
telegraphy. Two instruments must 
be tuned to the same pitch in order 
to be responsive. Thus an instru- 
ment sending out waves of 70,000 
vibrations cannot be recorded by 
one tuned much below or above 
the same number. 

Sound waves of sympathetic or 
harmonic vibrations. 

Currents, Positive. {See Positive 
Currents.) 

Cut-in. To electrically connect a 
piece of mechanism or a conductor 
with a circuit. 

Cut-out. The reverse of the cut- 
in. To remove from a circuit any 
conducting device. The cut-out 
may be so arranged as to leave the 
circuit complete in some other way. 

An appliance for removing a piece 
of apparatus from a circuit so that 
no more current shall pass through 
the former. 

Cut-out, Automatic. A safety de- 
vice for automatically cutting out 
a circuit to prevent accident or 
the burning -out of an apparatus, 
due to an overload of current. It 
is worked by an electro-magnet and 
spring. An overload of current 
causes a magnet of high resistance 
to draw an armature towards it, 
and this, in turn, releases the spring 
of the cut-out device. Sometimes 
a strip or wire of fusible metal is 
employed which is in circuit with 
a switch. The excess of current 
fuses the metal, and the broken cir- 
cuit releases a spring- jack, which, in 
turn, breaks the circuit. 

Cut-out, Safety. A block of non- 
conducting material, such as marble, 
slate, or porcelain, carrying a safety- 



377 



ELECTRICITY BOOK FOR BOYS 



fuse or plugs. In these is enclosed 
a piece of fusible wire, which bums 
out or melts and breaks the circuit 
before the apparatus is damaged. 

Cut-out, Wedge* A cut-out oper- 
ated by a wedge, such as a spring- 
jack or the plugs at the end of the 
flexible wires on the switch -boards 
of telephone exchanges. 



Damper. A frame of copper on 
which the wire in a galvanometer is 
sometimes coiled. It acts to check 
the needle oscillations. 

A brass or copper sheathing or 
tube placed between the primary 
and secondary coils of an induction- 
coil to cut off induction and dimin- 
ish the current and potential of the 
secondary circuit. When the tube 
is drawn out gradually the induc- 
tion increases. It is commonly 
used in medical coils to adjust their 
strength of action. 

D-C An abbreviation for direct 
current. 

Dead Earth. A fault in telegraph 
and telephone lines which consists 
in the ground-wire being improperly 
grounded, or not fully connected 
with the earth. 

Dead Tarns. A term applied to 
the ten to twenty per cent, of the 
convolutions or turns of wire on 
an armature which are considered 
to be dead. There are supposed to 
be about eighty per cent, of the 
turns on an armature that are ac- 
tive in magnetizing the core; the 
balance are outside the magnetic 
field and are termed dead, although 
they are necessary to the produc- 
tion of electro-motive force. 

Dead Wire. A wire in the elec- 
tric circviit through which no current 
is passing. 

A disused or abandoned electric 
conductor, such as a telegraph wire. 



or a wire which may be in circuit, 
but through which at the time of 
speaking no electrical action is tak- 
ing place. /'.; 

Death, Electrical. Death result- 
ing from an electric current passing 
through the animal body — electro- 
cution; accidental death by electric 
shock; premeditated death through 
bringing the body in direct contact 
with conductors carrying high elec- 
tro-motive force. High electro-mo- 
tive force is essential, and the alter- 
nating current is most fatal. 

Decomposition, Electrolytic. The 
decomposition or separation of a 
compound liquid into its constitu- 
ents by electrolysis. The liquid 
must be a conductor or electrolyte, 
and the decomposition is carried on 
by means of electricity. 

The conversion of two or more 
chemicals into a new compound or 
substance. 

Deflection. In magnetism, the 
movement of the needle out of the 
plane. It is due to disturbance, or 
to the needle's attraction towards 
a mass of iron or steel or another 
magnet. 

Demagnetization. The removal 
of magnetism from a paramagnetic 
substance. The process is principal- 
ly in use for watches which have be- 
come magnetized by exposure to the 
magnetic field surrounding d3''namos 
or motors. 

Density, Electric. The relative 
quantity of electricity, as a charge, 
upon a unit area of surface. It may 
be positive ot negative 

Surface density, as the charge of 
a Leyden-jar. 

Depolarization. A term applied 
to the removal of permanent mag- 
netism, such as that from a horse- 
shoe magnet, a watch, or a bar- 
magnet. Heat is the common de- 
polarizer, but counter electro-mag- 
netic forces are employed also in the 

78 



APPENDIX 



various forms of apparatus known 
as demagnetizers. 

Deposit, Electrolytic. The metal or 
other substances precipitated by the 
action of a battery or other current- 
generator, as in the plating processes. 

Detector. A portable galvanom- 
eter, by means of which a current 
and its approximate strength can 
be detected and measured. 

Diaphragm. In telephones and 
microphones, a disk of iron thrown 
into motion by sound-waves or by 
electric impulse. It is usually a 
thin plate of japanned iron, such as 
is used in the ferrotype photograph- 
ic process for making tin-types. 

Dielectric. Any substance through 
which electrostatic induction is al- 
lowed to occur, such as glass or rub- 
ber. It is a non-conductor for all 
electric currents. 

Dielectric Resistance. The resist- 
ance a body offers to perforation or 
destruction by an electric discharge. 

Dimmer. An adjustable choke or 
resistance coil used for regulating 
the intensity of electric incandes- 
cent lamps. It is employed exten- 
sively in theatres for raising or low- 
ering the brilliancy of lights. 

Dipping. The process of clean- 
ing articles by dipping them in acids 
or caustic soda, preparatory to elec- 
tro-plating. 

Simple immersion, with or with- 
out current, to put a blush of metal 
on a cleaned surface. 

Dipping-needle. A magnetic nee- 
dle mounted on a horizontal bear- 
ing so that it will dip vertically 
when excited by a current passing 
horizontally about it. The ordinary 
compass-needle is mounted on a 
point, and swings freely to the right 
or left only. 

Direct Current. {See Current, 
Direct.) 

Discharge. The eruptive dis- 
charge from a Ley den- jar or accumu- 



lator of a volume of electricity stored 
within it. 

The abstraction of a charge from 
a conductor by connecting it to the 
earth or to another conductor. 

Discharge, Disruptive. The dis- 
charge of a static charge through a 
dielectric. It involves the mechani- 
cal perforation of the dielectric. 

Disconnect. To break an electric 
circuit or open it so as to stop the 
flow of current; to remove a part 
of a circuit or a piece of apparatus 
from a circuit. 

Distillation, Electric. The dis- 
tilling of a liquid by the employment 
of electricity, which, by electrifying 
the liquid, assists the effects of heat. 
It is asserted that the process is 
accelerated by the electrification of 
the liquid or fluid, but it must be a 
conductor liquid or electrolyte. Oil, 
being a non-conductor, is not affect- 
ed by any electric current, no matter 
what its specific gravity may be. 

Distributing Centre. The centre 
of distribution in a system having 
branch circuits, such as the electric- 
light or telephone outlets from a 
main station. 

Door - opener, Electric. A mag- 
netic contrivance arranged in con- 
nection with a lock, by means of 
which the latch is released by press- 
ing a distant push - button. This 
device is used in flats and apart- 
ment-houses for opening a door 
from any of the apartments in the 
house. 

Double Filament Lamp. An in- 
candescent lamp having two fila- 
ments, one with a high capacity, the 
other with a low one. The high 
capacity may be from sixteen to 
fifty candle-power, the other from 
one to five. A turn of the bulb in 
its socket, or the pulling of a string 
which operates a switch in the 
socket, cuts out the current from 
the long filament and sends it 



379 



ELECTRICITY BOOK FOR BOYS 



through the shorter and finer one, Earth - plate* A plate buried it^ 

thus giving a weaker Hght. These the ground to receive the ends oj 

"hy-lo" lamps are useful as night telegraph lines and other circuits, 

lamps in halls, bath-rooms, or in and so give a ground connection! 

sick-rooms, where a low or weak light Copper plates are often used, but 



is required all night. 



in houses the ground is usually 



Doable Pole -switch, A cut-out formed by attaching a wire to the 
that is arranged to cut out the cir-' gas or water pipes. 



cuit of both the negative and posi- 
tive leads at the same time. 



Earth Return* The grounding 
of a wire in a circuit at both ends 



Doable - pash. A contact - push gives the circuit an earth return, 

having two contacts and arranged This method is commonly used in 

so that pressure upon it opens one telegraph lines, both in the wire 

contact and closes the other. and wireless systems. 

Doable Throw-switch* A" switch Eddy Carrents. {See Currents, 

so arranged that it can be thrown Eddy.) 

into either one of two contacts; a Edison Distribating-box. A box 

throw-over switch. used in the Edison "three-wire" 

Driving-palley* The broad-faced system, from which the outlets pass 

or channelled pulley on an armature to local circuits. 

shaft by means of which the power Edison Lalande Cell. A zinc-cop- 
from a motor may be transmitted per battery having a depolarizing 
mechanically. coating of copper oxide on the cop- 
Dry Battery* {See Battery, Dry.) per element, the couple being im- 
Dact* The space in an under- mersed in an electrolyte composed 
ground conduit for a single wire or of potash or caustic soda, 
cable. Ediswan. A term applied to the 
Duplex Wire. An insulated con- incandescent lamps invented by Edi- 
ductor having two distinct wires son and Swan and used extensively 
twisted or laid together, but prop- in Great Britain. Also applied to 
erly insulated from each other. other apparatus designed by the 

Dynamic Electricity* Electricity two inventors, 
in motion or flowing, as distinguished Efficiency* The relation of work 

from static or frictional electricity. done to the electrical energy ab- 

Electricity of relatively low po- sorbed. The efficiency is not equal 

tential or electro - motive force in to the energy absorbed, because it 

large quantity or amperage. always takes more power to gener- 

Dynamo* An apparatus con- ate a current than is given back in 



sisting of a core and field-magnets, 
propeiiy wound with insulated wire, 
which, when put into operation by 



actual efficiency. This is due to 
mechanical friction and to the re- 
sistance of the air in a mechanism 



revolving the core or armature at such as a dynamo when revolving at 
high speed, develops electric current ; high speed. 



a mechanical generator of_electricity 

Dynamo, Motor, 
dynamo.) 



Earth* The accidental grounding 
of a circuit is termed an "earth." 



Efficiency, Electrical* In a gen- 
{See Motor- erator it is the total electrical ener- 
gy produced, both that wasted and 
that actually used in driving ma- 
chinery or apparatus. 

Efflorescence* The dry salts on 
a jar or vessel containing liquid that 

380 



APPENDIX 



collects above the water or evapora- 
tion line. This is due to creeping. 

Elasticity. A property in some 
bodies and forces through which they 
recover their former figure, shape, 
or dimensions when the external 
pressure or stress is removed. Water 
has no elasticity. Air is very elas- 
tic; steam has a great volume of 
elasticity; while electricity is un- 
doubtedly the most elastic of all in 
its motion through air, water, and 
other conducting mediums. 

Electric. Pertaining to electric- 
ity; anything connected with the 
use of electricity. It has been a 
much-abused word, and its meaning 
has been garbled by the impostor, 
the crook, and the ' ' business thief ' ' 
in foisting on the public wares in 
which there was no electrical prop- 
erty whatever. "Electric" tooth- 
brushes, combs, corsets, belts, and 
the like may contain a few bits of 
magnetized steel, but they possess 
no active therapeutic value. 

Electrical Engineer. The pro- 
fession of electrical engineer calls 
for the highest knowledge of elec- 
tricity, both theoretical and practi- 
cal. It embraces the designing and 
installation of all kinds of electrical 
apparatus. 

Electrician. One versed in the 
practices and science of electricity; 
a practical lineman or wireman. 

Electricity. One of the hidden 
and mysterious powers of nature, 
which man has brought under con- 
trol to serve his ends, and which 
manifests itself mainly through at- 
traction and repulsion; the most 
powerful and yet the most docile 
force known to man, coming from 
nowhere and without form, weight, 
or color, invisible and inaudible ; 
an energy which fills the universe 
and which is the active principle 
in heat, light, magnetism, chemical 
affinity, and mechanical motion. 

38 



Electricity, Atmospheric. The 

electric currents of the atmosphere, 
variable but never absent. They 
include lightning, frictional electric- 
ity, the Aurora Borealis, the electric 
waves used in wireless telegraphy, 
etc. Benjamin Franklin indi- 
cated the method of drawing elec- 
tricity from the clouds. In June, 
1752, he flew a kite, and by its 
moistened cord drew an electric 
current from the clouds so that 
sparks were visible on a brass key 
at the ground end of the cord. Later, 
when a fine wire was substituted for 
the cord, and a kite was flown in a 
thunder - storm, the electric spark 
was vivid. This experiment con- 
firmed his hypothesis that lightning 
was identical with the disruptive 
discharges of electricity. 

Electricity, Latent. The bound 
charge of static electricity. 

Electricity, Negative. {See Nega- 
tive Electricity.) 

Electricity, Positive. {See Posi- 
tive Electricity.) 

Electricity, Voltaic. Electricity 
of low potential difference and large 
current intensity. 

Electricity produced by a voltaic 
battery or dynamo as opposed to 
static electricity, which is friction- 
al and practically uncontrollable for 
commercial purposes. 

Electrification. The process of im- 
parting an electric charge to a sur- 
face. The term is applied chiefly to 
electro-static phenomena. 

Electrization. In electro - thera- 
peutics, the subjection of the human 
system to electric treatment. An 
electric tonic imparted by electro- 
medical baths through the nervous 
system. 

Electro-chemistry. That branch 
of science which treats of the rela- 
tions between electric and chemical 
forces in their different reactions and 
compounds. It deals with electro- 



ELECTRICITY BOOK FOR BOYS 



plating, electro - fusing, electrolysis, 
etc. 

Electro-cttltare. The application 
of electricity to the cultivation of 
plants. The use of electricity has 
been found very beneficial in some 
forms of plant growth. 

Electroctftion, Capital punish- 
ment inflicted by electric current 
from a dynamo of high electro- 
motive force. The current used is 
from 1500 to 2000 volts, and it 
acts to break down the tissues of 
the body. 

Electrode. The terminals ' of an 
open electric circuit. 

The terminals between which an 
electric arc is formed, as in the arc- 
Hght. 

The terminals of the conductors of 
an electric circuit immersed in an 
electrolytic solution, such as the 
carbon and zinc of a battery. 

Electrolier. A fixture for sup- 
porting electric lamps, similar to a 
chandelier for gas or candles. Com- 
bination electroliers conduct both 
gas and electricity. 

Electrolysis. The separation of a 
chemical compound into its con- 
stitutent parts by the action of an 
electric current. 

Electrolyte. A body susceptible 
of decomposition by the electric cur- 
rent. It must be a fluid body and 
a conductor capable of diffusion as 
well as composite in its make-up. 
An elemental body such as pure 
water cannot be an electrolyte. 

Electrolytic Decomposition. (See 
Decomposition, Electrolytic.) 

Electrolytic Deposit. {See De- 
posit, Electrolytic.) 

Electrolytic Resistance. (See Re- 
sistance, Electrolytic.) 

Electro-magnetic Induction. (See 
Induction, Electro-Magnetic.) 

Electro - magnetism. Magnetism 
created by electric current. 

That branch of electrical science 



which treats of the magnetic rela- 
tions of a field of force produced 
by a current. 

Electro - medical Bath. A bath 
provided with connections and elec- 
trodes for causing a current of elec- 
tricity to pass through the body of 
the patient. 

Electrometer. An instrument 
used for measuring static electricity. 
Electrometers are different from gal- 
vanometers, since the latter depend 
on a current flowing through wires 
to create an action of the magnetic 
needles. 

Electro - motive Force. Voltage. 
It may be compared to the pressure 
of water in hydraulic systems. The 
unit of electro-motive force is the 
volt. 

Electro - motor. A term some- 
times applied to a current-generator, 
such as a small dynamo or voltaic 
battery. 

Electro - plating. (See Plating, 
Electro.) 

Electropoion Flwid. An acid de- 
polarizing solution for use in zinc- 
carbon couples, such as the "Gre- 
net" and "Daniells" cells. The bi- 
chromate-of-potash and sulphuric- 
acid solution for battery charges is 
a good example. 

Electroscope. An apparatus for 
indicating the presence of an elec- 
tric charge and whether the charge 
is negative or positive. 

Electrostatic Acctimwlator. Two 
conducting surfaces, separated by 
a dielectric and arranged for the op- 
posite charging of the two surfaces. 
A faradic or static machine for ac- 
cumulating frictional electricity is 
an example. 

Electrostatics. That division of 
electric science which treats of the 
phenomena of the electric charge, or 
of electricity in repose, as contrasted 
with electro-dynamics or electricity 
in motion. 



382 



APPENDIX 



Electrotype* The reproduction 
of a form of type or engraving by 
the copper electro-plating process. 
The original is coated with plum- 
bago and a wax impression taken of 
it. The face of the negative is made 
conductive with plumbago or tin 
dust, then suspended in a copper 
bath and connected with the current. 
A film of copper will be deposited 
on the face of the wax impression. 

Element, ChemicaL Original 
forms of matter that cannot be" 
separated into simple constitutents 
by any known process. There are 
about seventy in all, but as science 
advances the list is constantly being 
revised. New elements are dis- 
covered and known ones are being 
resolved into simpler forms. 

Elements of Battery Cell. {See 
Battery Cell, Elements of.) 

Emergency Switch. An auxiliary 
switch used as a controller on a car 
to reverse the action of the motor. 

E-M-F. An abbreviation for elec- 
tro-motive force, or voltage. 

Equalizer. A term applied to a 
wire or bar in electro-magnetic mech- 
anism for equalizing the pressure 
over a system. 

Exciter. A generator used for ex- 
citing the field-magnets of a dyViamo. 

Extension Call-bell. A bell con- 
nected with a telephone call-bell, and 
located in another part of a building 
so as to give a distant summons. 

External Circttit. {See Circuit, 
External.) 



F. The sign commonly employed 
to designate Fahrenheit. Thus, 30° 
F. means 30 degrees Fahrenheit, or 
30 degrees above zero. 

False Magnetic Poles. {See Mag- 
netic Poles, False.) 

Faradic. Induced current pro- 
duced from induction - coils and 
faradic machines. 



A series of alternating electro- 
static discharges, as from a Holtz 
influence machine. 

Faradic Coil. {See Coil, Faradic.) 

Faradic Currents. {See Currents, 
Faradic.) 

Faradic Machine. An apparatus 
designed to produce faradic current. 

Feed. To furnish an electric cur- 
rent, also spoken of in connection 
with the mechanism that moves the 
carbons in arc -lamps. 

Feeders, or Feed Wires. The con- 
ductors which convey electric cur- 
rents at different points, as in the 
trolley system. The current is car- 
ried along in large cables strung on 
poles or laid underground, and at 
proper distances lines are run in to 
feed the trolley wire. 

Field. The space in the neigh- 
borhood of a dynamo or motor, or 
other generator of electric current, 
from which the apparatus takes its 
electricity, both electrostatic and 
magnetic. 

Field-magnet. {See Magnet, 
Field.) 

Field of Force. The space in the 
neighborhood of an attracting or 
repelling mass or system. There 
are two kinds of fields of force — the 
electro-magnetic and the static— 
from which the respective pieces of 
apparatus draw their store of elec- 
tricity. 

Filament. A long, thin piece of 
solid substance. It is generally as 
thin as a thread and flexible enough 
to be bent. 

The hairlike element in an in- 
candescent lamp which, when heated 
by a current, glows and radiates light. 

Filaments, Paper. Filaments for 
incandescent lamps made of car- 
bonized paper. They were the ones 
originally used in electric lamps, but 
have been superseded by other sub- 
stances easier to handle and more 
durable. 



3^3 



ELECTRICITY BOOK FOR BOYS 



Flow. The volume of a current 
or stream escaping through a con- 
ductor, such as a wire, rod or pipe. 

Fluorescence. The property of 
converting ether waves of one length 
into waves of another length. The 
phenomenon is utilized in the pro- 
duction of Geissler tubes and X-rays. 

Fluoroscope. An apparatus for 
making examinations by means of 
the X-rays. 

Fluoroscopic Screen. A screen 
overspread with fluorescent material 
and employed for fluoroscopic ex- 
aminations in connection with the 
X-rays. 

Foucault Currents. {See Cur- 
rents, Foucault.) 

Force. Any change in the con- 
dition of matter with respect to 
motion or rest. Force is measured 
by the acceleration or change of 
motion that it can impart to a body 
of a unit mass in a unit of time. For 
instance, ten pounds pressure of 
steam will be indicated on a gauge 
made for measuring steam. That 
pressure of steam, with the proper 
volume behind it, is capable of in- 
stantly producing a given part of a 
horse-power. In the same way ten 
volts of electro-motive force is capa- 
ble of pushing a current so as to ex- 
ert a certain fraction of horse-power. 

Force, Electro -magnetic. The 
force of attraction or repulsion ex- 
erted by the electro-magnet. It is 
also known as electric force in the 
electro-magnetic system. 

Fractional Distillation. The proc- 
ess of evaporating liquids by heat, 
the most volatile being the first 
treated. When that has been evapo- 
rated and distilled the heat is raised 
and the next most volatile liquid is 
evaporated, and so on until all are 
evaporated, leaving as a residue the 
solids that were a part of the origi- 
nal mass of liquid. 

Friction, The effect of rubbing, 



or the resistance which a moving 
body encounters when in contact 
with another body. 

Frictional Electricity. Electric- 
ity produced by the friction of dis- 
similar substances. 

Frictional Electric Machine. An 
apparatus for the development or 
generation of high-tension frictional 
electricity. 

Full Load. A complete load. 
The greatest load a machine or 
secondary battery will carry per- 
manently. The fidl capacity of a 
motor running at its registered 
speed for its horse-power. 

Furnace, Electric. A furnace in 
which the heat is produced by the 
electric arc. It is the hottest fur- 
nace known to man, and tempera- 
tures as high as 7500° Fahrenheit 
have been developed in it. 

Fuse, Electric. A fuse for ignit- 
ing an explosive charge by elec- 
tricity. It is made by bringing the 
terminals or ends of wires close to- 
gether, so that they will spark 
when a current passes through them. 
Or a thin piece of highly resistant 
wire may be imbedded in an ex- 
plosive and brought to white heat 
by current. 

Fuse-block. An insulator having 
a safety-fuse made fast to it. 

Fuse - box. A box containing a 
safety-fuse, generally of porcelain, 
enamelled iron, or some other non- 
conductor. 

Fuse -links. Links composed of 
strips or plates of fusible metal 
serving the purpose of safety-fuses. 

Fusing-current. A current of suf- 
ficient strength to cause the blowing 
or fusing of a metal. 



Galvanic. Voltaic, Relating to 
current electricity or the electro- 
chemical relations of metals. 



384 



APPENDIX 



Galvanic Taste. A salty taste in 
the mouth resulting from the pas- 
sage of a light current from a voltaic 
battery, the ends of the wires being 
held to either side of the tongue. 
This has been called tasting elec- 
tricity, but it is really the decom- 
position of saliva on the surface of 
the tongue, due to electrolysis or 
the passage of a current through a 
liquid. 

Galvanism. The science of voltaic, 
or current, electricity. 

Galvanizing. Coating iron with 
a thin layer of zinc by immersing the 
object in the molten metal. 

Galvano-faradic. In medical elec- 
tricity the shocking-coil. The appli- 
cation of the voltaic current, induced 
by a secondary current (induction- 
coil) , to any part of the body. 

Galvanometer. An instrumxCnt for 
measuring current strength. 

A magnetic needle influenced by 
the passage of a current through a 
wire or coil located near it. 

Galvanometer, Tangent. A gal- 
vanometer provided with two mag- 
netic needles differing in length, the 
shorter one serving to measure tan- 
gents, the longer being used for sine 
measurements of current strength. 

Galvanoscope. An instrument, 
generally of the galvanometer type, 
used to ascertain whether a current 
is flowing or not. 

Generator. An apparatus for main- 
taining an electric current, such as 
a dynamo, a faradic machine, a bat- 
tery, etc. 

German-silver. An alloy of cop- 
per, nickel, and zinc. Used chiefly 
in resistance-coils, either in the form 
of wire or in strips of the sheet- 
metal. 

Gold - bath. A solution of gold 
used for depositing that metal in the 
electro-plating bath. 

Graphite. A form of carbon. It 
occurs in nature as a mineral, and 



also is made artificially by the 
agency of electric heat. 

Gravity Battery. (See Battery, 
Grayity.) 

Grounded Circtfit. (See Circuit, 
Grounded.) 

Ground -plate. (See Plate, 
Ground.) 

Ground -wire. The contact of a 
conductor, in an electric circuit, 
with the earth. It permits the es- 
cape of current if another ground- 
wire exists. 

Guard Tube. A tube inserted in 
a wooden or brick partition to in- 
sulate wires that may pass through 
it. These tubes are made of por- 
celain, gutta - percha, compositions 
of a non - conducting nature, and 
fibre. 

Gtitta-percha. Caoutchouc treat- 
ed with sulphur to harden it; some- 
times called vulcanized rubber or 
vulcanite. It is a product obtained 
from tropical trees, and when prop- 
erly treated it is a valuable insulator 
in electrical work, particularly in sub- 
marine cables, since it offers great 
resistance to the destructive agencies 
of the ocean's depths. 

H 

Hand Generator. A magneto-gen- 
erator driven by hand for the gener- 
ation of light currents. 

Harmonic Currents. {See Cur- 
rents, Harmonic.) 

Harmonic Receiver. A receiver 
containing a vibrating reed acted on 
by an electro-magnet. Such a reed 
answers only to impulses tuned to its 
pitch. 

Heat. One of the force agents of 
nature. It is recognized in its effects 
through expansion, fusion, evapora- 
tion, and generation of energy. 

Heat, Electric. Caused by a re- 
sisting medium, such as carbon or 
German-silver, when too much cur- 



aS 



38s 



ELECTRICITY BOOK FOR BOYS 



rent is forced through it. The prin- 
ciple of the car-warmers, electric iron, 
electric chafing-dish, etc. 

Helix. A coil of wire. Properly 
a coil of wire so wound as to follow 
the outlines of a screw without over- 
laying itself. 

Horse-power, Electric* Meaning 
the same as in mechanics. Referred 
to when speaking of the working 
capacity of a motor or the power 
required to drive a dynamo. 

Horse -power Hour. A unit or 
standard of electrical work theoret- 
ically equal to that accomplished by 
one horse during one hour. 

Horseshoe Magnet. {See Magnet, 
Horseshoe.) 

H-P. Abbreviation for horse- 
power. 

Hydrometer. An instrument em- 
ployed to determine the amount of 
moisture in the atmosphere. 

An instrument for determining 
through flotation the density or 
specific gravity of liquids and fluids. 
It consists of a weighted glass bulb 
or hollow metallic cylinder with a 
long stem on which the Baume 
scale is marked. Dropping it into 
a liquid it floats in a vertical posi- 
tion, and sinks to a level consistent 
with the gravity of the fluid. 

Hydrometer, Baume. An ap- 
paratus for testing the gravity of 
fluids. The zero point corresponds 
to the specific gravity of water for 
liquids heavier than water. A 
gauge, valuable in testing acids and 
other fluids used in electrical work. 



Igniter. A mechanical hand ap- 
paratus, in which a battery, induc- 
tion-coil, and vibrator are located, 
and whose spark, jumping across a 
gap at the end of a rod, ignites or 
lights a gas flame, blasting-powder, 
or dynamite. 



I-H-P. An abbreviation for in- 
dicated horse-power. 

Illtiminating Power. Any source 
of light as compared with a stand- 
ard light— as, for instance, the illu- 
minating power of an electric light 
reckoned in candle-power. 

Illamination. A light given from 
any source and projected on a sur- 
face, per unit of area, directly or by 
reflection. It is stated in terms — 
as, for instance, the candle-power of 
a lamp. When speaking of an in- 
candescent lamp we say it illumi- 
nates equal to four candle-power 
or it gives a light equal to sixteen 
.candle-power. 

Immersion, Simple. Plating, with- 
out the aid of a battery, by simply 
immersing the metal in a solution 
of metallic salt. 

Impulse. The motion produced 
by the sudden or momentary action 
of a force upon a body. An electro- 
magnetic impulse is the action pro- 
duced by the electro-magnetic waves 
in magnetizing a mass of soft iron 
and attracting to it another mass 
of iron or steel. 

An electro-motive impulse is one 
where the force rises so high as to 
produce an impulsive discharge such 
as that from a Ley den- jar. 

Incandescence, Electric. The 
heating of a conductor to red or 
white heat by the passage of an 
electric current. For example, an 
incandescent lamp. 

Incandescent Circuit. (See Cir- 
cuit, Incandescent.) 

Incandescent Lamp -filament. 
(See Filament.) 

India-rubber. (See Caoutchouc 
and Gutta-percha.) 

Indicator-card. The card used 
in galvanoscopes, volt and ampere 
meters, and other instruments. It 
is provided with a moving needle 
and is marked with a graduated 
scale. 



386 



APPENDIX 



Induced. Caused by induction, wire composing an induction-coil 

and not directly. are the best and simplest examples 

Induced Cttrrent. {See Current, of electro-magnetic induction. 
Induced.) Induction, Magnetic. The mag- 

Indtictance. That capacity of a netization of iron or other para- 
circuit which enables it to exercise magnetic substances by a magnetic 
induction and create lines of force, field. The magnetic influence of a 

Inductance is the ratio between bar excited under these conditions 

the total induction through a circuit is shown by throwing iron filings 

to the current producing it. upon it. They will adhere to both 

Induction, Back. A demagnetiz- ends (that is at the negative and 
ing force produced in a dynamo positive poles) but not at the mid- 
armature when a lead is given to the die. 

brushes. When the brushes are so Inductor. A mass of iron in a 
set the windings on the armature current generator which is moved 
are virtually divided into two sets: past a magnet-pole to increase the 
one a direct magnetizing set, the number of lines of force issuing there- 
other a cross-magnetizing set which from. It is generally laminated, and 
exerts a demagnetizing action on is used in inductor dynamos and mo- 
the other set. The position of the tors of the alternating-current type, 
brushes on a dynamo or motor is Influence, Electric. Electric in- 
indicated by their location, and if duction or influence which may be 
changed back induction will be the electro-static, current, or electro- 
result, magnetic. 

Induction-coil. (See Coil, Indue- Influence Machine. A static elec- 
tion.) trie machine worked by induction. 

Induction, Electro - magnetic, and used to build up charges of op- 
When negative and positive cur- posite nature on two separate prime- 
rents are brought towards each oth- conductors. 

er against their material repulsive Installation. The entire appara- 

tendencies the result is work, or tus, building, and appurtenances of 

energy, and the consequent energy a technical or manufacturing plant 

increases the intensity of both cur- or power-house. An electric-light 

rents temporarily. The variations installation would mean the machin- 

thus temporarily produced in the ery, street-lines, lamps, etc. 
currents are examples of electro- Insulating Joint. Used for the 

magnetic induction. A current is purpose of insulating a gas -pipe 

surrounded by lines of force. The from an electric circuit, 
approach of two circuits — one nega- Insulating Varnish. A varnish 

tive, the other positive — involves a composed of insulating material, 

change in the lines of force about such as gums, shellac, or diluted rub- 

the secondary circuit. Lines of ber. Shellac dissolved in alcohol is 

force and current are so intimately perhaps the best. It is easy to 

connected that a change in one make and dries quickly, making an 

compels a change in the other, insulating surface practical for al- 

Therefore, the induced current in most every ordinary use. 
the secondary may be attributed to Insulation. The dielectric or non- 

the change in the field of force in conducting materials which are used 

which it lies. The inner and outer to prevent the leakage of electricity, 

coils of wire about the soft iron The covering for magnet wires, and 

387 



ELECTRICITY BOOK FOR BOYS 



overhead conduits for power lines 
and electric lighting. 

Insulation, OiL Any non- com- 
bustible oil may be employed as an 
insulator to prevent electrical leak- 
age in induction-coils, transformers, 
and the like. Its principal advan- 
tage lies in its being in liquid form, 
permitting of easy handling. More- 
over, if pierced by a spark from a 
coil, it at once closes again without 
becoming ignited. A solid insulator, 
if pierced, is permanently injured. 

Insulator, Any insulating sub- 
stance or material to prevent the 
escape of current. The knobs of 
porcelain or glass to which wires 
are made fast. 

Insulator, Porcelain. An insula- 
tor made of porcelain and used to 
support a wire. 

Intensity. The intensity or 
strength of a current is its amper- 
age. The strength of a magnetic 
field, its power to attract or mag- 
netize. 

Internal Circuit. {See Circuit, 
Internal.) 

Internal Resistance. (See Re- 
sistance, Internal.) 

Interrupter. A circuit - breaker. 
Any device which breaks or inter- 
rupts a circuit. It may be operated 
by hand or automatically. 

The vibrator of an induction-coil. 

The commutators of an arma- 
ture. 

Isolated Plant. The system of 
supplying electric energy by inde- 
pendent generating dynamos for 
each house, factory, or traction line. 

Isolation, Electric. A term ap- 
plied to "electric sunstroke." Ex- 
posure to powerful arc-light pro- 
duces effects resembling those 'of 
sunstroke. 

J 

Joint. The point where two or 
more electric conductors join. 



Joint Resistance. The united 
resistance offered by a number of 
resistances connected in parallel. 

Jumper. A short circuit-shunt 
employed temporarily around an 
apparatus, lamp, or motor to cut 
out the current. 

Jump-spark. A disruptive spark 
excited between two conducting sur- 
faces in distinction from a spark ex- 
cited by a rubbing contact. 

K 

Kaolin. A form of earth or prod- 
uct of decomposed feldspar com- 
posed of silica and alumina. It is 
serviceable in insulating compounds. 

Kathode. The terminal of an 
electric circuit whence an electrolyz- 
ing current passes from a solution. 
It is the terminal connected to the 
zinc pole of a battery or the article 
on which the electro-deposit is 
made. 

Key. The arm of a telegraphic 
sounder by which the circuit is 
made and broken. A pivoted lever 
with a finger-piece which, when de- 
pressed, makes contact between a 
point and a stationary contact on 
the base. 

Keyboard. A board, or table, on 
which keys or switches are mounted. 

A switchboard. 

Kilowatt. A compound unit ; one 
thousand watts; an electric-current 
measure. Abbreviation, K-W. 

Kilowatt Hour. The result in 
work equal to the expenditure or 
exertion of one kilowatt in one hour. 

Kinetoscope. A photographic in- 
strument invented by Edison for 
obtaining the effect of a panorama 
or moving objects by the display of 
pictures in rapid succession — in fa- 
miliar parlance, "moving pictures." 

Knife Switch. A switch with a 
narrow and deep, movable blade, or 
bar of copper or brass, which re- 



SS8 



APPENDIX 



sembles the blade of a knife. It is 
forced between two spring-clamps 
attached to one terminal so as to 
make perfect contact. 

L 

Laminated. Made up of thin 
plates, as an armature-core. 

Laminated Core* (See Core, Lami- 
nated.) 

Lamp-Arc. A lamp in which the 
light is produced by a voltaic arc. 
Carbon electrodes are used, and a 
special mechanism operates and 
regulates the space between the 
carbons so that a perfect arc may 
be maintained. 

Lamp, Incandescent. A lamp in 
which the light is produced through 
heating a filament to whiteness by 
the electric current. It consists of 
a glass bulb from which the air is 
exhausted and sealed, after the 
filament is enclosed. The ends of 
the filament are attached to plati- 
num wires, which in turn are made 
fast to the contact-plates at the 
head of the lamp, so as to connect 
with the current. 

Lamp - socket. A receptacle for 
an incandescent lamp. It is gen- 
erally made of brass and provided 
with a key-switch to turn the cur- 
rent on and off. 

Latent Electricity. {See Electric- 
ity, Latent.) 

Lead. (Not the metal.) An in- 
sulated conductor which leads to 
and from a source of power; an 
insulated conductor to and from a 
telegraph or telephone instrument; 
a circuit, a battery, or a station. 
Not a part of the line circuit. 

That part of an electric light or 
power circuit which leads from the 
main to the lamps or motors. 

Lea ding-in "Wires. The wires 
which lead into a building from an 
aerial circuit. 



The wires which lead in and out 
from a lamp, battery, or instrument. 

Leak. An escape of electrical en- 
ergy through leakage. This is more 
liable to occur in bare than in in- 
sulated wires. The escape of cur- 
rent from bare trolley wires is much 
greater than that from the insulated 
conductors, particularly in damp or 
rainy weather. 

Leclanche Battery. (See Battery, 
Leclanche.) 

Ley den-jar. A type of static con- 
denser. Its usual form is a glass 
jar. Tin - foil is pasted about its 
inner and outer surfaces covering 
about half the wall. The balance 
of the glass is painted with shellac 
or insulating varnish. The mouth 
is closed with a cork stopper, and 
through its centre a brass rod is 
passed which, by a short chain, is 
connected with the interior coating 
of the jar. The top of the rod is pro- 
vided with a brass knob or ball, and 
from this last the spark is drawn. 

Lightning. The electro-static dis- 
charge of clouds floating in the at- 
mosphere. It is the highest form 
of frictional electricity, uncontrol- 
lable and very dangerous, since the 
strength of a single flash may run 
into hundreds of thousands of volts. 

Lightning - arrester. An appara- 
tus for use with electric hnes to carry 
off to earth any lightning discharges 
that such lines may pick up; or it 
may be a form of fuse which bums 
out before the current can do any 
harm to the electrical mechanism. 

Line-insttlator. An insulator serv- 
ing to support an aerial line. 

Lineman. A workman whose 
business is the practical part of elec- 
trical construction in lines and con- 
ducting circuits. 

Link -fuse. A plate of fusible 
metal in the shape of a link. It is 
used as a safety-fuse in connection 
with copper terminals. 

389 



ELECTRICITY BOOK FOR BOYS 



Liquefaction, Electric. The con- 
version of a solid into a liquid by 
the sole agency of electricity in its 
heat action upon the solid. 

Liquid Resistance. {See Resist- 
ance, Liquid.) 

Lithanode. A block of com- 
pressed lead binoxide, with platinum 
connections, for use in a storage 
battery. 

Litharge. Yellow-lead. A chemi- 
cal form of metallic lead. 

Load. In a dynamo, the am- 
peres of current delivered by it un- 
der given conditions of speed, etc. 

Local Action. In a battery, the 
loss of current due to impurities in 
the zinc. The currents may circu- 
late in exceedingly minute circles, 
but they waste zinc and chemicals 
and contribute nothing to the effi- 
ciency of the battery. 

In a dynamo, the loss of energy 
through the formation of eddy cur- 
rents in its core or armature, in the 
pole pieces, or in other conducting 
bodies. 

Lodestone. The scientific name 
is magnetite. Some samples possess 
polarity and attract iron ; these are 
called lodestones. 

Loop. A portion of a circuit in- 
troduced in series into another cir- 
cuit. 

Low Frequency. A frequency (in 
current vibrations) of comparatively 
few alternations per second. 

Low Potential Current. (See Cur- 
rent, Low Potential.) 

Luminescence. The power or 
properties some bodies have of giv- 
ing out light when their molecular 
mass is excited. For example, phos- 
phorus and radium. 

Luminous Heat. The radiation 
of heat by electric current, which at 
the same time produces light. For 
example, the filament in an incan- 
descent lamp. 

Luminous Jar. A Leyden-jar 



whose coatings are of lozenge-shaped 
pieces of tin-foil between which are 
very short spaces. When discharged, 
sparks appear all over the surface 
where the small plates of metal near- 
ly join. 

M 

Magnet. A substance or metal 
having the power to attract iron 
and steel. 

Magnet -bar. A magnet in the 
shape of a straight bar. (See Bar- 
magnet.) 

Magnet-coil. A coil of insulated 
wire enclosing a core of soft iron 
through which a current of elec- 
tricity is passed to magnetize the 
iron. 

Magnet - core. An iron bar or 
mass of iron around which insulated 
wire is wound in order to create an 
electro-magnet. 

Magnet, Electric. A magnet con- 
sisting of a bar of iron, a bundle of 
iron wires, or an iron tube, around 
which a coil of insulated wire is 
wound. When a current is pass- 
ing through the coil its influence 
magnetizes the iron core, but direct- 
ly the current ceases the magnetism 
disappears. 

Magnet, Field. The electro or 
permanent magnet in a dynamo or 
motor, used to produce the area of 
electric energy. 

Magnet, Horseshoe. A magnet 
of U shape with the poles or ends 
brought closer together than the 
other parts of the limbs. A soft 
iron bar is placed across the poles 
when not in use, as this serves to 
conserve the magnetism. 

Magnet, Permanent. A term ap- 
plied to a hard steel magnet possess- 
ing high retentivity, or the power to 
hold its magnetism indefinitely. 

Magnet, Regulator. An electro- 
magnet whose armature moves in 
such a manner as to automatically 



390 



APPENDIX 



shift the commutator - brushes, on 
a motor or dynamo, to a position 
which insures the preservation of 
both brushes and commutator-bars, 
and also produces a constant cur- 
rent. 

Magnet, Simple. A magnet made 
of one piece of metal. 

Magnetic Adherence. The ten- 
dency of a mass of iron to adhere to 
the poles of a magnet. 

Magnetic Attraction and Repul- 
sion. The attraction of a magnet 
for iron, steel, nickel, and cobalt; 
also of unlike poles of magnets for 
each other. The like poles repel. 

Magnetic Circtiit - breakers. An 
automatic switch, or breaker, whose 
action is excited and controlled by 
an electro-magnet. 

Magnetic Concentration of Ores. 
The separation of iron and steel 
from their gangue by magnetic at- 
traction. It is applic'able only when 
either the ore or the gangue is sus- 
ceptible to the magnet. 

Magnetic Control. The control of 
a magnetic needle, magnet, index, 
armature, or other iron indicator in 
a galvanometer, ammeter, or volt- 
meter by a magnetic field. 

Magnetic Dip. The inclination 
from the horizontal position of a mag- 
netic needle that is free to move in 
a vertical plane. 

Magnetic Field, Rotary. A mag- 
netic field resulting from a rotary 
current. 

Magnetic Field, Shifting. A mag- 
netic field which rotates. Its lines 
of magnetic force vary, therefore, in 
position. 

Magnetic Field, Uniform. A field 
of uniform strength in all portions, 
such as the magnetic field of the 
earth. 

Magnetic Force. The power of at- 
traction and repulsion exercised by 
a magnet ; the force of attraction and 
repulsion which a magnet exercises, 



and which, in its ultimate essence, is 
unknown to science. 

Magnetic Induction. {See Induc- 
tion, Magnetic.) 

Magnetic Needle. A magnet hav- 
ing a cup or small depression at its 
centre, and poised on a sharp pin of 
brass, so as to be free to rotate. Its 
N pole points to the north, and its 
S pole to • the south. A compass 
needle. 

Magnetic Poles. The terrestrial 
points towards which the north or 
south poles of the magnetic needle 
are attracted. There are two poles: 
the arctic, or negative, which at- 
tracts the positive or N pole of the 
magnetic needle; and the antarctic, 
or positive, w^hich attracts the S pole 
of the needle. 

Magnetic Poles, False. It has 
been established that there are oth- 
er poles on the earth that attract the 
magnetic needle when the latter is 
brought into their vicinity. These 
are called false poles, and are prob- 
ably caused by large deposits of 
iron lying close to the surface of the 
earth. 

Magnetic Separator. An appara- 
tus for separating magnetic sub- 
stances from mixtures. It is used 
chiefly in separating iron ore from 
earth and rock. The mineral falls 
on an iron cylinder, or drum, mag- 
netized by coils, and adheres there, 
while the earth or crushed rock 
drops below. The particles of iron 
are afterwards removed by a scraper. 
The machine is also used in separat- 
ing iron filings and chips from brass, 
copper, or other metals, the iron 
adhering to the magnet, while the 
brass and other chips drop under- 
neath. 

Magnetism. The phenomena of at- 
traction exerted by one body for 
another. It has been commonly 
understood that magnetism and 
electricity are very closely related, 



391 



ELECTRICITY BOOK FOR BOYS 



for without electricity magnetism 
could not exist, although it has not 
been shown clearly that magnetism 
plays any part in the generation of 
electricity. Magnetism is the phe- 
nomenal force exerted by one body 
having two poles (negative and posi- 
tive) for like bodies. The horse- 
shoe magnet or a bar of magnetized 
steel are the simplest examples of 
this. If both ends of the horseshoe 
were positive they would not at- 
tract, but would repel. If both 
ends of a bar were positive they 
would repel; but as one is negative, 
or north-seeking, and the other posi- 
tive, they exert lines of force which 
attract like bodies, such as bits of 
iron, nails, and needles. No energy 
is required to maintain magnetism 
in a tempered steel object, such as 
the wiring about a soft iron core 
when it has been magnetized, but 
electric current must flow about the 
soft iron core in order to render it 
a magnet. So soon as the current 
ceases to flow the magnetism cases 
and the soft iron fails to attract. 

Magnetism, Uniform. Magnetism 
that is uniform throughout a mass 
of magnetic steel, or a core that is 
electro-magnetic. 

Magnetize. To impart magnetic 
property to a substance capable of 
receiving it. 

Magnetizing-coil. {See Coil, Mag- 
netizing.) 

Magneto Call -bell. A call -bell 
used principally in telephone sys- 
tems, and operated by a current 
from a magneto-electric generator. 
The current is excited by turning 
the handle at the side of the tele- 
phone-box before removing the re- 
ceiver from the hook. 

Magneto - generator. A current- 
generator composed of a permanent 
magnet and a revolving armature 
which is rotated between the poles 
of the permanent magnet. 



Magnet "Wire. Insulated wire ^ 
used for coils. Cotton or silk cov- 
ered wire is the most serviceable for 
winding magnets. 

Main Circuit. (See Circuit, Main.) 

Main Feeder* The main wire in 
a district to which all the feeder 
wires are attached. 

Main Switch. The switch con- 
nected to the main wire of a line, 
or the main-switch controlling a 
number of auxiliary switches. 

Mains, Electric. The large con- 
ductors in a system of electric light 
or power distribution. 

Make and Break, Atitomatic. An 
apparatus which enables the arma- 
ture of a magnet to make and break 
its circuit automatically. 

Make - and - break Current. {See 
Current, Make-and-break.) 

Merctirial Air - pttmp. An air- 
pump operated by mercury to 
obtain a high vacuum, and used 
extensively for exhausting incan- 
descent-lamp bulbs. 

Mercury Tube. A glass tube 
sealed and containing mercury. It 
is so arranged as to give out fluores- 
cent light when shaken or agitated 
by an electric current. For example, 
the Geissler tubes, the Cooper-Hewitt 
light. Crook's tubes, etc. 

Metallic Arc. An arc which forms 
between metallic electrodes. 

Metallic Circuit. {See Circuit, 
Metallic.) 

Metallic Conductor. A conductor 
composed of a metal. 

Metallic Filament. A metal wire 
used in an incandescent lamp — the 
filament. 

Metallic Resistance. {See Resist- 
ance, Metallic.) 

Metallurgy. The art of working 
metals. Electro-metallurgy applies 
to the processes wherein electricity 
plays the most important part. 

Mica. A natural mineral- of sheet 
form and translucent, used exten- 



392 



APPENDIX 



sively as an insulator in electrical 
equipment and mechanism. 

Mica, Moulded. A composition 
composed of ground mica and shel- 
lac as a binder. When heated and 
pressed into various shapes and 
forms, it is a valuable insulator, and 
is employed for hooks, locks, tubes, 
sockets, and the like. 

TVIicanite. An insulating material 
made by cementing laminations of 
pure mica together and cementing 
them with shellac or other suitable 
non-conducting adhesives. 

Molecalar Adhesion, The attrac- 
tion of similar molecules for each 
other. 
f Molecalar Attraction, The at- 

traction of molecules, or physical 
affinity. 

Molectilar Resistance. The resist- 
ance which a mass or electrolyte 
offers when contained in an insu- 
lated vessel and a current of elec- 
tricity is passed through it. 

Molecule. One of the invisible 
particles supposed to constitute 
matter of every kind; the smallest 
particle of matter that can exist 
independently. It is made up of 
atoms, but an atom cannot exist 
alone 

Morse Receiver. The receiving 
instrument once universally used in 
the Morse system of telegraphy, but 
now superseded by the sounder. 

Morse Recorder. An apparatus 
which automatically records on a 
ribbon of paper the dots and dashes 
of the Morse telegraph alphabet. 

Morse Sounder. An electro-mag- 
netic instrument designed to make 
a sharp, clicking sound when its 
armature lever is drawn down by 
the attraction of the magnets. 

Morse System. A telegraphic 
system invented by Prof. S. F. B, 
Morse, in which, by means of alter- 
nating makes and breaks of varying 
duration, the dots and dashes of the 



Morse alphabet are reproduced and 
received at a distance through the 
agency of wires and the electro-mag- 
netic sounder. 

Motor, Electric. A machine or 
apparatus for converting electric en- 
ergy into mechanical kinetic energy 
or power. The electrical energy is 
usually generated by a dynamo, and 
distributed on Conductors to motors 
located at various points. 

Electric motors are of two types 
— the A-C, or alternating current, 
and the D-C., or direct current. 

Motor-car, Electric. A self-pro- 
pelling car driven by stored elec- 
tricity. 

Motor - dynamo. A motor driv- 
en by a dynamo whose armature is 
firmly attached or connected to 
that of the dynamo. It is used for 
modifying a current. If the dynamo 
generates an alternating current of 
high potential, the motor converts 
it into a direct current of lower volt- 
age but increased amperage. 

Motor-transformer. A transform- 
er which is operated by a motor. 

A dynamo-electric machine pro- 
vided with two armature windings, 
one serving to receive current, as a 
motor, the other to deliver current, 
as a generator, to a secondary cir- 
cuit. 

N 

N. An abbreviation for the north- 
seeking pole in a magnet. 

Natural Magnet. A loadstone. 

Needle. A term applied to a bar- 
magnet poised horizontally upon a 
vertical point. 

A magnetic needle, or the magnet 
in a mariner's compass. 

Negative. Opposed to positive. 

Negative Electricity. The kind of 
electricity with which a piece of 
amber is charged by friction with 
flannel. 

In a galvanic battery or cell the 



393 



ELECTRICITY BOOK FOR BOYS 



surface of the zinc is charged with 
negative electricity. Negative elec- 
tricity, according to the theory of 
some scientists, really means a de- 
ficiency of electricity. 

Negative Electrode. The same as 
Negative Element. 

Negative Element. The plate not 
dissolved by the solution in a vol- 
taic cell ; the one which is positively 
charged. 

The carbon, platinum, or copper 
plate or pole in a battery. 

Negative Feeder. The conductor 
which connects the negative mains 
with the negative poles of a gen- 
erator. 

Negative Plate. (See Plate, Nega- 
tive.) 

Negative Pole. (See Pole, Nega- 
tive.) 

Netttral Feeder. The same as 
Neutral Wire. 

Neutral "Wire. The central wire 
in a three-wire system. 

Nickel -bath. A bath for the 
electro-deposition of nickel. 

Non- arcing Fuse. A fuse -wire 
which is enclosed in a tube packed 
with asbestos or silk, and which 
does not produce an arc when it 
fuses or blows out. It is practically 
noiseless, save for a slight hissing 
sound, accompanied by a light puff 
of smoke, which escapes from a vent- 
hole in the side of the tube. 

Non - conductor. A material or 
substance offering very high resist- 
ance to the passage of the electric 
current. 

Non -magnetic Steel. Alloys of 
iron incapable of being magnetized. 
They are composed of iron and man- 
ganese, nickel, steel, etc. 

Normal. Regular. The average 
value of observed quantities. Nor- 
mal current is a regular current with- 
out, variations. 

The force of a current at which a 
system is intended to work. 



Normal Voltage. The same as 
Normal Current. 

North Pole. The north - seeking 
pole of a magnet. 

The pole of a magnet which tends 
to point to the north, and whence 
lines of force are assumed to issue 
on their course to the other pole of 
the magnet. 



0. An abbreviation for Ohm. 

Oersted^s Discovery. Oersted dis- 
covered, in 1820, that a magnetic 
needle tended to place itself at 
right angles to a current of elec- 
tricity. This fundamental princi- 
ple is the basis of the galvanometer, 
the dynamo, and the motor. 

Ohm. The practical unit of re- 
sistance. A legal ohm is the re- 
sistance of a column of mercury one 
square millimetre in cross-sectional 
area and 106.24 centimetres in 
length. 

Ohm, True. The true ohm is the 
resistance of a column of mercury 
106.24 centimetres long and one 
square millimetre in cross-sectional 
area. An ohm may be measured by 
a No. 30 copper wire nine feet and 
nine inches long. If larger size wire 
is used the piece must be proportion- 
ately longer, since the resistance is 
less. 

Ohmic Resistance. True resist- 
ance as distinguished from spurious 
resistance, or counter electro - mo- 
tive force. {See also Resistance, 
Ohmic.) 

Ohm*s Law. The basic law which 
expresses the relations between cur- 
rent, electro - motive force, and re- 
sistance in active circuits. It is for- 
mulated as follows: 

1. The current strength is equal 
to the electro - motive force divided 
by the resistance. 

2. The electro-motive force is 



394 



APPENDIX 



equal to the current strength mul- 
tipHed by the resistance. 

3. The resistance is equal to the 
electro-motive force divided by the 
current strength. 

0» K. A telegraphic signal mean- 
ing yes, or all right. It is supposed 
to be a misspelled form of all cor- 
rect, "Oil Kerrekt." 

Okonite. A form of insulation 
for wires and conductors; a trade 
name applied to insulations, and pro- 
tected by copyright. 

Open Arc* A voltaic arc not en- 
closed. 

Open Circuit. (See Circuit, Open.) 
/ Oscillating Current. (See Current, 
Oscillating.) 

Outlet. That part of an elec- 
trolier or electric light fixture out 
of which the wires are led for at- 
tachment to incandescent light sock- 
ets. 

Outside "Wiring. The wiring for 
an electric circuit which is located 
outside a building or other struct- 
ure. 

Overhead Feeders. The same as 
overhead conductors. 

Overhead Trolley. The system 
in which the current for the pro- 
pulsion of trolley-cars is taken from 
overhead feeders or wires. 

Overhead TroIIey-wire. A naked, 
hard copper wire drawn at high ten- 
sion, and suspended over or at the 
side of a car-track, and from which 
the trolley- wheel takes its current. 

Overload. In an electric motor, 
an excess of mechanical load pre- 
vents economical working, causing 
the armature to revolve slowly and 
the wiring to heat. In this case 
heating implies waste of energy. 

Overload Switch. A switch which 
operates automatically to open a 
circuit in line with a motor, and so 
save the motor from overheating or 
burning in the event of an over- 
load. 



Paper Cable. A cable insulated 
with waxed or paraffined paper. 

Paraffine. A residuum of petro- 
leum oil, valuable as an insulating 
medium in electrical work. 

A hydro - carbon composition of 
the highest resistance known. It is 
extensively used in condensers and 
other electrical apparatus as a di- 
electric and insulator. 

Parallel Distribution. A distrib- 
uting system for electricity where- 
in the receptive contrivances are 
adjusted between every two of a 
number of parallel conductors run- 
ning to the limits of the system. 
When two or more conductors con- 
nect two mains of comparatively 
large size and low resistance, they 
are said to be in parallel or in multi- 
ple. This order is easily pictured 
by imagining the mains to be the 
sides of a ladder and the conductors 
the rungs. In the latter the lamps 
are placed. It follows that the cur- 
rent flows from one main to the other 
through the conductors and lamps. 

Paramagnetic. Substances which 
have magnetic properties, or those 
which are attracted by magnetic 
bodies. A paramagnetic substance 
has high multiplying power for lines 
offeree, therefore a bar of iron which 
is a paramagnetic substance of the 
highest quality becomes magnetic 
when placed within a circle of elec- 
tric lines of force. The first example 
of paramagnetic substance brought 
to the attention of man was the lode- 
stone, from which the ancient mari- 
ners fashioned their crude compass 
needles. 

P-C. An abbreviation for porous 
cup. 

Pear Push. A push-button en- 
closed in a handle having the shape 
of a pear. It is generally attached 
to the end of a flexible wire cord. 



395 



ELECTRICITY BOOK FOR BOYS 



Periodic Current. (See Current, 
Periodic.) 

Permanency, Electric. The pow- 
er of conductors to retain their con- 
ductivity unaffected by the lapse 
of time. 

Permanent Magnet. (See Mag- 
net, Permanent.) 

Phase. One complete oscillation. 
The interval elapsing from the time 
a particle moves through the mid- 
dle point of its course to the instant 
when the phase is to be stated. 

Simple harmonic motion. Oscil- 
lation. 

'Phone. An abbreviation for the 
word Telephone. 

Phonograph. An apparatus for 
reproducing sound. It is vibratory 
and not electric in its action, except 
that the mechanism may be driven by 
electricity. It consists of a rotat- 
ing cylinder of a waxlike material 
and a glass diaphragm carrying a 
needle - point that lightly touches 
the surface of the waxen cylinder. 
If the diaphragm is agitated the 
needle vibrates, making indenta- 
tions in the surface of the wax. If 
the needle is set back and the cylin- 
der rotated so as to cany the point 
over the indentations, the sound is 
given back through the vibration of 
the diaphragm. 

Pickle. An acid solution used to 
cleanse metallic surfaces preparatory 
to electro-plating. 

Pilot "Wires. Wires brought from 
distant parts of electric light and 
power mains, and leading to volt- 
meters at a central station. Through 
their agency the potential energy of 
every part of the system may be 
measured. 

Pith-balls. Balls made from the 
pith of light wood, such as elder. 
They are used in the construction 
of electroscopes and for other ex- 
periments in static electricity. 

Plant. The apparatus for gen- 



erating electric current, including 
engines, boilers, dynamos, mains, 
and subsidiary apparatus. 

Plate, Condenser. In a static 
apparatus, the condenser having a 
flat piece of glass for a dielectric. 
It is mounted on an axle so that it 
may be revolved. 

Plate, Ground. In a lightning-ar- 
rester, the plate connected to the 
earth or ground wire. 

Plate, Negative. In a voltaic 
battery, the plate which is unat- 
tacked by the fluid. It is made of. 
carbon, platinum, or copper. 

Plate, Positive. {See Positive 
Plate.) 

Plating -bath. A vessel of solu- 
tion for the deposition of metal by 
electrolysis. Used in electro-plat- 
ing. 

Plating, Electro. The process of 
depositing metal on surfaces of 
metals or other substances by the 
aid of an electrolyte and the elec- 
tric current. 

Platinum Fuse. A slender wire 
of platinum roused to incandescence 
by current, and used to explode a 
charge of powder or other combus- 
tible substance. 

Plug. A piece of metal, with a 
handle, used to make electric con- 
nections by being inserted between 
two slightly separated plates or 
blocks of metal. 

A wedge of metal, slightly taper- 
ed, and used to thrust between two 
conductors to close or complete a 
circuit. 

Plumbago. Soft, lustrous graph- 
ite a native; form of carbon some- 
times chemically purified. It is used 
chiefly in electrotyping for dusting 
the wax moulds to make the surface 
an electric conductor. 

Plunge - battery. {See Battery, 
Plunge.) 

Polar. Pertaining to one of the 
poles of a magnet. 



396 



APPENDIX 



Polarity. The disposition in a 
body to place its axis in a particular 
direction when influenced by mag- 
netism. For example, the attrac- 
tion and repulsion at the opposite 
ends of a magnet. The N and S 
seeking poles of a compass needle is 
the simplest example. 

Polarity, Electric. The d i s p o s i - 
tion in a paramagnetic body to be 
influenced by electric waves and 
lines of force. The otherwise non- 
magnetic body or mass becomes 
piagnetic to attract or repulse when 
influenced by electricity, but ceases 
to retain the phenomena after the 
electric influence is removed. A 
piece of soft iron wire, a nail, or a 
short rod of iron will become electro- 
polarized when a current of elec- 
tricity is sent through a coil of in- 
sulated wire so wound that one end 
will be N the other S. So soon as 
the circuit is broken the polarity 
ceases. 

Polarization. The depriving of a 
voltaic cell of its proper electro- 
motive force. This may be brought 
about through the solution becoming 
spent, or in the event of the acid 
being saturated with zinc, and so 
failing to act on the metallic zinc. 

Counter electro-motive force due 
to the accumulation of hydrogen on 
the negative plate. 

Polarizing-ctirrent. (See Current, 
Polarizing.) 

Polar Surface. The surface of a 
magnetic substance through which 
the magnetic flux passes in or out. 

Pole-changer. An automatic, os- 
cillating switch or contact-breaker 
which reverses the direction of the 
current. 

Pole, Negative. The S pole in a 
magnet or compass needle. 

Pole, Positive. (See Positive 
Pole.) 

Pole-switch, Single. A switch de- 
signed to open or close one lead only. 



Poles. The terminals of an open 
electric circuit at which there neces- 
sarily exists a potential difference. 

The terminals of an open magnetic 
circuit, or the ends of a magnetized 
mass of iron. 

Porcelain. A fine variety of earth- 
enware, valuable for insulators and 
insulating purposes.- 

Porosity. The state or property 
of having small interstices or holes. 
The opposite of density. 

Porous Cup or Cell. A cup or 
cell made of pipe -clay or of un- 
glazed earthenware through which 
a current of electricity can pass 
when wet or in a liquid. Porous 
cups are used in cells and batteries 
to keep two liquids apart, and yet 
permit electrolysis and electrolytic 
conduction. 

Positive Currents. Currents which 
deflect the needle to the left. 

Positive Electricity. The current 
that flows from the active element, 
the zinc in a battery, to the carbon. 
The negative electricity flows from 
the carbon to the zinc. 

Positive Electrode. The electrode 
which is connected with the positive 
pole of a source of electric energy. 

Positive Feeders. The lead or 
wire in a set of feeders which is con- 
nected to the positive terminal of 
the generator. 

Positive Plate. In a voltaic cell, 
the plate which is acted upon and 
corroded. The current from the 
positive plate is negative electricity. 

Positive Pole. The N pole in a 
magnet or magnetic needle. So 
called because it seeks the north 
or negative pole of the earth. 

Positive Wire, or Conductor. The 
wire, or conductor, connected with 
the positive pole of any apparatus 
which produces electro-motive force. 

Potential, Electric. The power to 
perform electric work. 

Potential Energy. Capacity for 



397 



ELECTRICITY BOOK FOR BOYS 



doing work. Potential energy when 
liberated becomes actual energy for 
the performance of work. 

Power - generator* Any source 
from which power is generated. 

Power-house. A station in which 
the plant of an electric power sys- 
tem is operated and the current dis- 
tributed to local or long - distance 
points. Power - houses are either 
primary or secondary stations. In 
the primary station the current is 
generated directly by the aid of 
mechanical power, either the steam- 
engine or the steam-turbine. The 
secondary station, or sub-station, 
is located at a distance from the 
main power-house, and has no me- 
chanical means of generating cur- 
rent. The current, usually of high 
alternating voltage, is supplied to 
the sub-station from the main power- 
house; and by means of transform- 
ers and converters, the high-voltage 
current is transformed into one of 
lower E-M-F and higher amperage, 
for distribution over local lines. 

Power-unit. The unit of electric 
power is the volt-ampere or watt. 

Pressure, Electric. Electro - mo- 
tive force or voltage. 

Primary. A term used to desig- 
nate the induction - coil in an in- 
duction - apparatus or transformer. 
It is an abbreviation for primary 
coil. 

Primary Battery. (See Battery, 
Primar}^) 

Prime Conductor. (See Conduc- 
tor, Prime.) 

Push-button. A switch for clos- 
ing a circuit by means of pressure 
applied to a button. The button 
is provided with a spring, so that 
when pushed in and released it flies 
back, reopening the circuit. 

Pyrogravure. A process of en- 
graving by the use of platinum points 
heated to redness by the electric 
current. 



Q. Abbreviation or symbol for 
electric quantity. 

Quadrant. The quarter of a cir- 
cle or of its circumference. 

Quadruple Circuit. (See Circuit, 
Quadruple.) 

Quantity. The term is applied 
to express arrangements of elec- 
trical connections for giving the 
largest possible amovmt of current. 

Quantity, Electro-magnetic. The 
electro-magnetic current measured 
by its intensity for a second of time. 

Quick-break. A break affected in 
an electric current by the employ- 
ment of a quick-break switch. 

Quickening. The amalgamating 
of the surface of a metallic object 
before electro-plating it with silver. 
This secures better adhesion of the 
deposit, and is done by dipping the 
article into a solution of mercurial 
salts — one part of mercuric nitrate 
to one hundred parts of water. 



Radiant Energy. Energy exist- 
ing in the luminiferous ether and 
exercised in wave transmission , creat- 
ing light or sound. Radium possesses 
the highest form of radiant energy. 

Radiate. To emit or send out in 
direct lines from a point or points, 
as radiating heat, light, or sound. 
The radiations are sent out in all 
directions from a central point, just 
as a stone thrown in a pond of still 
water will radiate waves or ripples 
from the central point. 

Radiation. The travelling or mo- 
tion of ether waves through space. 

Radiator, Electric. A series of 
plates or wire-coils heated by cur- 
rent. They radiate heat and so 
warm the surrounding air. 

Radiograph. A photographic pict- 
ure taken by the X-ray process. 



398 



APPENDIX 



Receiver. In telephony or teleg- 
raphy, an instrument for receiving 
the message as distinguished from 
the instrument sending or trans- 
mitting the message. 

The telephone piece held to the 
ear is the receiver. 

Receiving End. The end of a 
line where the operative currents 
are received, as opposed to the end 
at which they are transmitted. 

Receptacle. A device for the in- 
stallation of an attachment or ex- 
tension plug. Used in connection 
with electric-lighting circuits. 

Recoil Kick. Reaction resulting 
from a disruptive discharge. 

Recorder. In telegraphy, the re- 
ceiving apparatus for recording the 
dot-and-dash signals on a strip or 
tape of paper. 

Redaction. The influence exert- 
ed without apparent communication 
by a magnetic field or a charged 
mass upon neighboring bodies. The 
induction-coil is a simple example of 
this force. The current passes through 
the primary or inner coil about a core 
of soft iron, and in doing so it develops 
lines of force in the secondary or outer 
coils, although no current is flowing 
directly through them from a battery 
or dynamo. 

Redaction Gear. A gear which 
acts to reduce a speed below that of 
a motor in full motion without les- 
sening its motive force. 

Refract. To break the natural 
course of light in an elastic medium. 
The rays of light, as they pass from 
a rare into a dense medium, are re- 
fracted. 

Register, Electric. An apparatus 
for registering and recording the 
movements of employes about a 
building. Press - buttons are ar- 
ranged throughout the building, and 
when a man passes a station he press- 
es the button, and the time is re- 
corded by the apparatus. 



Regulator Magnet. (See Mag- 
net, Regulator.) 

Relay. A telegraphic or tele- 
phonic receiving instrument which 
opens and closes a local circuit 
through movements caused by the 
impulses of currents received. The 
relay battery may be very delicate 
so as to work with weak currents. 
The function of the relay is to open 
and close circuits for the admission 
of a new current to push on the 
sound or vibration to a more dis- 
tant point. The main battery may 
be of any desired power. 

Relay Connection. A connection 
used in telegraphy, including a local 
battery, with a short circmt, nor- 
mally open, but closed at will by a 
switch and sounder, or other ap- 
pliance. A very weak current will 
work the apparatus. 

Relay, Ordinary. A relay that is 
not polarized. 

Relay, Repeating. In telegraphy, 
a relay for repeating the signals 
through a second line. 

Reluctance. Magnetic resistance. 

Repeater. In telegraphy, an in- 
strument for repeating the signals 
through a second line. It is virtual- 
ly a relay which is controlled by the 
sender, and which, in turn, operates 
the rest of the main line. It is 
usually located at about the middle 
of the total distance covered. 

Repeating - station. A telegraph 
station located on a long line, and 
occupying a position at the juncture 
of the sections into which the line 
is divided. The currents received 
through one section are repeated into 
the other sections by means of a 
repeater. 

Repulsion, Electric. The tenden- 
cy which exists between two bodies 
charged alike to mutually repel each 
other. 

Residual Charge. {S?e Charge, 
Residual.) 



399 



ELECTRICITY BOOK FOR BOYS 



Resilience. The power to spring 
back to a former position. Elec- 
tricity is resilient, although its elas- 
ticity cannot be measured accu- 
rately. 

Resin. A solid inflammable sub- 
stance or gum, and a good non-con- 
ductor in electrical work. It is the 
product obtained by distilling the 
sap of the pitch-pine. The name is 
also applied to the product of distill- 
ing the sap of other trees. Common 
resin, shellac, lac. Dragon's-blood, 
and other substances of a similar 
nature are resins. They are all di- 
electrics, and the source of negative 
frictional electricity when rubbed 
with cotton, wool, flannel, silk, or 
fur. 

Resistance. That quality of an 
electric conductor in virtue of which 
it opposes the passage of an electric 
current, causing the disappearance 
or modification of electro - motive 
force, and converting electric energy 
into heat energy. 

Resistance - box. A box filled 
with resistance-coils connected in 
series and provided with a switch, 
so that any number of the coils may 
be cut out. 

Resistance, Carbon. A resistance 
composed of carbon as a substitute 
for a coil of wire. Carbon rods are 
placed close together having an air 
space between them, with alternate 
ends connected. Piles may be built 
up of carbon plates, whose resistance 
.is made to vary by changing the 
pressure. 

Resistance - coil. A coil of wire 
metal or other substances having 
the power to resist a current of 
electricity. 

A coil of wire used to measure an 
unknown resistance by virtue of its 
own known resistance. (See also 
Coil, Resistance.) 

Resistance, Dielectric. (See Di- 
electric Resistance.) 



Resistance, Electrolytic. The re- 
sistance of an electrolyte to the pas- 
sage of a current decomposing it. It 
is almost entirely due to electrolysis, 
and is intensified by counter-electro- 
motive force. When a current of 
a voltage so low as not to decom- 
pose an electrolyte is passed through 
the latter, the resistance appears 
very high and sometimes almost in- 
finite. If the voltage is increased 
until the electrolyte is decomposed 
the resistance suddenly drops to a 
point lower than the true resistance. 

Resistance, Internal. The resist- 
ance of a battery, or generator, in 
an electric circuit as distinguished 
from the resistance of the rest of 
the circuit. 

Resistance, Liqttid. A liquid of 
varying specific gravity used to 
create resistance to the passage of 
the electric current. 

Resistance effected by the use of 
liquid through which a current must 
pass to complete a circuit. 

Resistance, Metallic. The resist- 
ance of metals to the electric current. 

German - silver resistance as dis- 
tinguished from that of water, car- 
bon, or other substa,nces. 

Resistance, Ohmic. True resist- 
ance measured in ohms as distin- 
guished from counter electro-motive 
force. (See also Ohmic Resistance.) 

Resistance, Sptiriotis. The coun- 
ter-electro-motive force. In its effect 
of opposing a current and in resist- 
ing its formation it differs from 
true resistance. True resistance di- 
minishes current strength, absorbs 
energy, and develops heat. Spurious 
resistance opposes and diminishes a 
current without absorption of energy 
or production of heat. 

Resistance, Standard. A known 
resistance employed to determine un- 
known resistances by comparison. 

Resistance, True. The true re- 
sistance measured in ohms as dis- 



400 



APPENDIX 



tinguished from counter - electro- 
motive force. 

Resonator, Electric. A small, 
open electric circuit with ends nearly 
touching. When exposed to elec- 
tric resonance, or to a sympathetic 
electric oscillating discharge, a spark 
passes across the gap. The spark 
is due to inductance in the resonator. 

Retentiveness. That property 
wHich enables steel to retain its 
magnetism. 

Retttrn. A line or conductor 
which carries current back to its 
starting-point after it has traversed 
a circuit. The best definition of a 
return is a circuit on which no new 
apparatus is installed. 

Ret«rn-circttit. (See Circuit, Re- 
turn.) 

Retttrn-circaitt Railway. A 
grounded circuit used in trolley 
systems for ground returns through 
the tracks, they being joined by 
links or flexible wires so as to form 
perfect conductors. It is the nega- 
tive side of the system, the posi- 
tive being in the overhead or under- 
ground feed-wire or rail. 

Reversibility. The principle by 
which any form of generator for pro- 
ducing a given form of energy may 
be reversed to absorb energy. The 
dynamo of the reversible type driven 
to generate current may be reversed 
and will develop power if a current 
is run through it. 

Rheostat. An adjustable resist- 
ance. An apparatus for changing 
the resistance, without opening the 
circuit, by throwing a switch-bar 
across contact points. 

Rod Clamp. A clamp used in the 
lamp rod of an arc-light to hold the 
carbon. 

Rontgen Effects. Phenomena 
obtained by the use of the X or 
Rontgen rays. 

Rontgen - ray Screen. A screen 
whose surface is covered with fluo- 



rescent material for the purpose of 
receiving and displaying the Ront- 
gen image. 

Rontgen Rays. A peculiar form 
of light radiation discovered by 
Rontgen, and which is emitted 
from that portion of a high vacuum 
tube upon which the kathode rays 
fall. 

Rotary Magnetic Field. (See 
Magnetic Field, Rotary.) 

Rahmkoff Coil. {See Coil, Ruhm- 
koff.) 



Safety Fase. A device to prevent 
overheating of any portion of a cir- 
cuit by excessive current. It gen- 
erally consists of a strip of fusible 
metal which, if the current attains 
too great strength, melts and opens 
the circuit. 

Salt. A chemical compound con- 
taining two atoms or radicals which 
saturate each other. One is electro- 
positive, the other electro-negative. 

Salts are decomposed by electrol- 
ysis, and in separating they combine 
to form new molecules. 

Saturated. A liquid is said to be 
saturated when it has dissolved all 
the salts it will take up. 

Search-light. An apparatus for 
producing a powerful beam of light 
and projecting it in any desired di- 
rection. 

Secondary. A term applied to 
the secondary coil of a transformer 
or induction-coil. 

Secondary Battery. (See Bat- 
tery, Secondary.) 

Secondary Plates. The plates of 
a secondary battery or storage-bat- 
tery. When charged, the negative 
plate should be brown or deep red- 
dish in color, and the positive slate- 
colored. 

Self - excited. Electrified by its 
own current. 

Self-winding Clock. A clock 



401 



ELECTRICITY BOOK FOR BOYS 



which automatically winds itself by 
electricity. It is operated by a 
small electro-magnetic motor which 
obtains its current from an outside 
source. 

Semaphore, Electric. An appara- 
tus for exhibiting signals. Used in 
the railway block system. 

Series. Arranged in succession. 
When incandescent lamps are in- 
stalled so that the current goes in 
and out of one lamp, and so on to 
the next and the succeeding ones, 
they are said to be arranged in 
series. It takes high E-M-F and 
current, or amperage, to operate 
such lamps. 

Series batteries are arranged with 
the zinc pole of one connected to the 
carbon pole of the next. 

Series Arc C«t-o«t. A device by 
means of which a short circuit is 
established past a defective lamp, 
thereby securing the undisturbed 
operation of all the other lamps in 
the circuit. 

Series Distribution. A distribu- 
tion of electricity in which the re- 
ceptive devices are arranged in suc- 
cessive order upon one conductor, 
extending the entire length of the 
circuit. 

Series Dynamo. A series-wound 
dynamo. 

Series Incandescent Lamp. An 
incandescent lamp adapted for ser- 
vice in a series circuit. 

Series Motor. A motor adapted 
for use in a series circuit; a motor 
whose field-coil winding is in series 
with the armature. 

Series, Maltiple. An arrangement 
of electric apparatus in which the 
parts are grouped in sets in paral- 
lel, and these sets are connected in 
series. 

Series "Winding. A method of 
winding a generator or motor in 
which one of the commutator brush 
connections is joined to the field- 



magnet winding. The other end of 
the magnet winding is connected 
with the outer circuit, and the sec- 
ond armature brush is coupled with 
the remaining terminal of the outer 
circuit. 

Service "Wires. Wires connected 
to the supply circuit or main wires, 
and which run into buildings to 
supply current for heat, light, and 
power. 

Shellac. A resin gum, gathered 
from certain Asiatic trees. It is 
soluble in alcohol, and is used ex- 
tensively in electric work as an 
insulator. 

Shifting Magnetic Field. {See 
Magnetic Field, Shifting.) 

Shock, Electric. The effect upon 
the animal system of the discharge 
of an electric current of high po- 
tential difference. The voltage is 
the main element in a shock. 

Shoe. As applied to electric 
railways, the casting employed to 
bear on the third rail to take in 
positive current and electro-motive 
force. 

The cast-iron plate of an electric 
break, which, by magnetism, adheres 
to another iron surface. 

Short Circtiit. (See Circuit, 
Short.) 

Sh«nt-box. A resistance-box de- 
signed for use as a galvanometer 
shunt. The box contains a series of 
resistance-coils which can be plugged 
in or out as required. 

Shunt - winding. A dynamo or 
motor is shunt-wound when the field- 
magnet winding is parallGl with the 
winding of the armature. 

Silver-bath. A solution of a salt 
of silver used in the electro-plating 
process. 

Silver-plating. Depositing a coat- 
ing of silver on a metallic surface by 
the acid of electro-metallurgy. 

Silver - stripping Bath. An acid 
solution used for stripping silver 



402 



APPENDIX 



from a metallic surface before re- 
plating it. 

Simple Circtiit. (See Circuit, 
Simple.) 

Simple Immersion. {See Immer- 
sion, Simple.) 

Simple Magnet. (See Magnet, 
Simple.) 

Single-troUey System. A trolley 
stystem employing only one over- 
head conducting wire, the track and 
ground serving as the return - cir- 
cuit. 

Single -wotmd Wire. Wire in- 
sulated by winding or overlaying 
with but a single layer of material. 

Sliding-condenser. (See Condens- 
er, vSliding.) 

.Snap -switch. A switch so con- 
trived as to give a quick break. A 
spiral spring is fastened between the 
handle and arm in such a manner 
that when the handle is drawn back 
the spring operates and quickly 
draws a knife-bar from the keeper, 
breaking the contact instantly and 
without the formation of an arc. 

Socket. A receptacle for an in- 
candescent lamp or plug. 

Solenoid. A helical coil of wire 
of uniform diameter or cylindrical 
in shape. It is useful in experi- 
ments with electro-magnetism. 

Soltition. A fluid composed of 
dissolved salts; a mixture of liquids 
and fluids. 

Sound Waves. Waves produced 
in an elastic medium by sonorous 
vibration, as in wireless telegraphy. 

Sounder. In telegraphy, the in- 
strumem: operated on by the key at 
the other end of a line. Various de- 
^ vices are employed to increase their 
vesonance — as, for instance, hollow 
boxes. Sounders are generally placed 
on local circuits and are actuated by 
relays. 

Soander, Repeating. A telegraph- 
ic instrument which repeats a mes- 
sage into another circuit. 



S-P. An abbreviation for single 
pole. 

Spark-arrester. A screen of wire- 
netting fitted around the carbons of 
arc -lamps to prevent the chips or 
hot sparks from flying. 

Spark - coil. A coil for produc- 
ing a spark from a source of com- 
paratively low electro-motive force. 
The induction-coil is an example. 

Spark, Electric. The phenonie- 
non observed when a disruptive 
charge leaves an accumulator or in- 
duction-coil and passes through an 
air gap. 

Spark-gap. The space left be- 
tween the ends of an electric reso- 
nator across which the spark springs. 

Sparking. The production of 
sparks at the commutator, between 
the bars and the brushes of dynamos 
and motors. They are minute vol- 
taic arcs, and should not be allowed 
to occur, as they cut away the metal 
and score the surface of the com- 
mutator. 

Spark -ttibe. A tube used as a 
gauge to determine v/hen the ex- 
haustion of the vacuum chamber, 
or bulb, of an incandescent lamp 
is sufficiently high. 

Specific Gravity. The relative 
weight or density of a body as com- 
pared with a standard. Water is 
usually taken as a standard for 
solids and liquids, and air for gases. 

Speed - cownter. An instrument 
which records the number of revo- 
lutions a shaft makes in a given time. 

Spent Acid. Acid which has be- 
come exhausted. In a battery the 
acid becomes spent from combina- 
tion with zinc; it also loses its de- 
polarizing power. 

Spring - contact. A spring con- 
nected to one lead of an electric 
circuit. It is arranged to press 
against another spring or contact, 
which it opens or closes by the in- 
troduction of a plug or wedge. 



403 



ELECTRICITY BOOK FOR BOYS 



Spring-jack. An arrangement of 
spring-arm conductors under which 
plugs with wires attached can be 
slipped to make a new connection 
or to cut out certain circuits. 

Spttriotis Resistance. (See Re- 
sistance, Spurious.) 

Standard Candle. (See Candle, 
Standard.) 

Standard Resistance. (See Re- 
sistance, Standard.) 

Starting - box. A resistance or 
shunt box used for letting current 
pass gradually into motors, instead of 
throwing on the full current at once. 

Static Electricity. Electricity 
generated by friction ; f rictional elec- 
tricity, such as lightning; electricity 
of high electro-motive force and prac- 
tically uncontrollable for commercial 
purposes. 

Static Shock. A term used in 
electro - therapeutics for describing 
the discharge from a small condenser 
or Leyden-jar; also the effect pro- 
duced by the action of the vibrator 
of the induction-coil. 

Station, Central. The building or 
place in which the electrical appa- 
ratus is installed for the generation 
of current ; the headquarters of tele- 
phone lines. 

Steady Current. An electric cur- 
rent whose strength is fixed or in- 
variable. 

Stock-ticker. An instrument em- 
ployed to give quotations of stocks 
by telegraphic record. A paper tape 
runs through an electrical machine 
which prints on it the figures and 
letters that stand for stocks and 
their values. The whole system is 
operated from a station located in 
the Stock-exchange. 

Storage Acctrnialator. {See Ac- 
cimiulator. Storage.) 

Storage - battery. {See Battery, 
Storage.) 

Strength of Current. Amperage; 
the quantity of current in a circuit. 



Stripping. The process of remov- 
ing electro - plating, or thin metal 
coatings, from an object before it is 
re-electro-plated. 

Stripping Liquid. The liquid in 
a stripping-bath used for removing 
metals from surfaces before replat- 
ing them. 

Submarine Cable. A telegraphic 
cable laid at the bottom of the sea 
or any body of water. 

Submarine Search-light. An in- 
candescent light which works under 
water. 

Sub - station. A generating or 
converting plant subsidiary to a 
central station, and placed so as to 
supply current in a district situated 
at a distance from the main power- 
house. 

Subway, Electric. An under- 
ground passageway utilized for car- 
rying cables and wires. 

Sweating. A process by which 
the ends of cables are brought to- 
gether and soldered. 

S - W - G. An abbreviation for 
standard wire gauge. 

Switch. A device for opening 
and closing an electric circuit. 
Made in a great variety of forms, 
such as push-button, telegraph-key, 
knife switch, automatic switch, lever 
switch, rheostat, etc. 

Switch -bell. A combined bell 
and switch. The bell is operated 
when the switch is opened or closed. 

Switch - blade. The blade of a 
switch; a conducting strip connect- 
ing two contact- jaws. 

Switch-board. A board or table 
to which wires are led and connect- 
ed with cross - bars or other de- 
vices by which connections can be 
made. 

Synchronize. To agree in point 
of time ; to effect concurrence of 
phase in two alternating - current 
machines, in order to combine them 
electrically. 



404 



APPENDIX 



Table-push, A push-button con- 
nected with a call-bell and fixed on 
a table for convenience in using. 

Tamadine. A form of cellulose 
used for making the filaments of in- 
candescent lamps. The material is 
cut into proper shapes, carbonized, 
and flashed. 

Tangent Galvanometer. {See 
Galvanometer, Tangent.) 

Tape, Insulating. Prepared tape 
used in covering the bared ends of 
wires or joints. 

Tap - wires. The conductors in 
trolley systems that at stated in- 
tervals, take the current from the 
mains and supply it to the bare feed- 
wires. 

Telegraph. A system of electric 
communication invented by S. P. 
B. Morse, in which the dot-and-dash 
characters are used. There are 
various modifications of the system 
— double (or duplex), multiplex, and 
quadruplex — by means of which a 
number of messages may be sent 
out over the same wires at one time. 
Communication from place to place 
is had over wires mounted on poles, 
or by underground or submarine 
cables. 

Telegraphy, "Wireless. A system 
of telegraphy carried on without the 
aid of wires, using instead the ether 
waves of the atmosphere to conduct 
the vibrations overhead, and the 
ground, or earth, as a return. The 
present limit of its working is about 
four thousand miles. 

Telephone. An instrument and 
apparatus for the transmission of 
articulate speech by the electric 
current. A magnet is encased in a 
tube and is encircled at one end by 
a coil of fine, insulated wire. A dia- 
phragm of thin iron is fixed in front 
of the coil and close to the end of 
the magnet. The ends of the coil- 



wires are connected with a line, at 
the other end of which another and 
similar instrument is installed. The 
voice causes the sending diaphragm 
to vibrate, and these waves are 
transmitted to the other instru- 
ment, where they can be heard 
through contra- vibrations of the re- 
ceiving diaphragm. 

Telephone, Long-distance. A 
telephone of modern construction, 
in which the sound-recording mech- 
anism is so sensitive as to make the 
vibrations of the voice audible at 
long distances. It will work satis-, 
factorily at one thousand or even 
fifteen hundred miles. 

Terminal. The end of any open 
electric circuit, or of any electric 
apparatus, as the electrodes of a 
battery. 

Thermostat, Electric. An ap- 
paratus similar in some respects 
to a thermometer, and used for 
closing an electric circuit when the 
latter becomes heated. It is used 
in connection with automatic fire- 
alarms to give warning of fire. For 
this purpose the metal coil is ar- 
ranged to close the contact at a 
temperature of 125° F. It usually 
consists of a compound strip of 
metal wound in the form of a spiral 
and fastened at one end. To this 
end one terminal of a circuit is con- 
nected. The expansion of the coil 
causes its loose end to touch a con- 
tact-point and close the circuit. 

Third Rail. A railway motive 
system which employs a third rail 
instead of an overhead trolley feed- 
wire. The rail is laid on or under 
the surface of the ground and prop- 
erly insulated. A shoe from the 
car bears on the rail and takes up 
the current. 

Three-wire Circuit. A system in- 
vented by Edison for the distribu- 
tion, from two dynamos, of current 
for multiple arc or constant poten- 



405 



ELECTRICITY BOOK FOR BOYS 



tial service. One wire or lead starts 
from the positive pole of one dyna- 
mo, another from the negative pole of 
the other dynamo, and between the 
two dynamos the central or neutral 
lead is made fast. 



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Now the dynamos may generate 
a current of 220 volts, and send it, 
at this strength, through the outer 
wires; but if lamps are connected 
between either of the outer and the 
neutral wires, the current, passing 
through the lamps, will be reduced 
to no volts. 

Time-ball, Electric. A ball which, 
by means of electricity, is made to 
drop from the top of a high pole, 
giving a visual signal for twelve 
o'clock or any other hour that may 
be designated. 

Traction, Electric. The propul- 
sion of a car or conveyance by means 
of electricity. 

Transformer. In alternating-cur- 
rent systems, the induction-coil by 
means of which the primary current, 
with high initial electro-motive force, 
is changed into a secondary current 
with low initial electro-motive force. 

Transmission. The conveyance of 
electric energy and currents from 
one point to another by the proper 
means of conduction. 

Transmitter. An instrument 
which originates the signals which 
are sent through a line or circuit. 
The Morse key in telegraphy and 
the Blake transmitter in telephony 
are examples. 

Tri-phase. Three-phase. 

Trolley. A contact - wheel of 
bronze which rolls under the sup- 
ply-wire in an overhead traction 



system and takes off the current 
necessary to run the car motors. 

TroIIey-wheel. The same as Trol- 
ley. 

TroIIey-wire. The overhead 
wire in a traction system which feeds 
the current through a trolley-wheel 
and pole to the motors of a car run- 
ning underneath. 

True Ohm. {See Ohm, True.) 

Trae Resistance. {See Resist- 
ance, True.) 

Two-wire Circuit. The single sys- 
tem universally used for light and 
power transmission of current. 

U 

Undulating Current. {See Cur- 
rent, Undulating.) 

Uniform Magnetic Field. {See 
Magnetic Field, Uniform.) 

Unipolar. Having but one pole. 

Unit. The single standard of 
force, light, heat, magnetism, attrac- 
tion, repulsion, resistance, etc. 



Vacuum. A space empty or void 
of all matter; a space from which 
all gases have been exhausted. 

Vacuum Tubes. Tubes of glass 
through which electric discharges are 
passed after the gases have been 
partially removed; for example, the 
X-ray tube of Rontgen and the 
Crooke tubes. 

Vibrator, Electro-magnetic. The 
make-and-break mechanism used on 
induction-coils, or other similar ap- 
paratus, in which, through alternate 
attractions, an arm or spring is kept 
in motion. 

Vitriol, Blue. A trade name for 
copper sulphate. (Bluestone.) 

Vitriol, Green. A trade name for 
ferrous sulphate. (Copperas.) 

Vitriol, White. A trade name for 
zinc sulphate. (Salts of zinc.) 



406 



APPENDIX 



Volt. The practical unit of elec- 
tro-motive force; the volume and 
pressure of an electric current. 

Voltage. Electric - motive force 
expressed in volts — as, a voltage of 
loo volts. 

Voltaic. A term derived from 
the name of the Italian scientist 
Volta, and used in many ways as 
applied to electrical current and de- 
vices. Formerly the term galvanic 
was commonly employed. 

Voltaic Electricity. {See Elec- 
tricity, Voltaic.) 

Voltimeter. An instrument for 
measuring the voltage of a current. 

Vulcanite. Vulcanized rubber. 
Valuable for its insulating properties 
and inductive capability. 

Watt. The practical unit of elec- 
trical activity; the rate of work or 
rate of energy. It is a unit of en- 
ergy or of work represented by a 
current of one ampere urged on by 
one volt of electro-motive force. 

The volt-ampere. 

The standard of electrical energy 
corresponding to horse-power in me- 
chanics. 

Watt -hoar. A unit of electric 
energy or work; one watt exerted 
or expended through one hour. 

Waves, Electro-magnetic. Ether 
waves caused by electro-magnetic 
disturbances affecting the luminifer- 
ous ether. 

Welding, Electric. Welding by 
the use of the electric current. 

Wimsharst Electric Machine. An 
influence machine for producing 
high potential or static electricity. 
Thin disks of glass are mounted on 
insulated bearings and revolved by 
power. Brushes collect the friction- 
al electricity, which is discharged 
into a Leyden-jar or other form of 



accumulator. It is of no practical 
use excepting in electro- therapeutics. 

Wire, Flexible. A cord of fine 
wire strands laid together and in- 
sulated so that it may be easily 
bent or wrapped. 

Wiring. Installing wires so as to 
form a circuit for the conveyance of 
current for light, heat, and power. 



X-rays. A curious phenomenon 
involving the radiation of invisible 
rays of Hght, which have the power 
to travel through various opaque 
bodies. The rays are used in de- 
tecting foreign substances in the 
human body and for photographing 
invisible or hidden objects without 
disturbing their surroundings. 

X - ray Lamp. A high vacuum 
tube lamp whose interior walls are 
covered with crystals of calcium or 
other fluorescent substances, and 
which, when exposed to the X-rays, 
give out a luminous light. 



Yoke. A piece of soft iron which 
connects the ends of two portions 
of a core on which wire coils are 
wound. It is located at the ends 
farthest from the poles. 

The soft-iron bar placed across 
the ends of a horseshoe magnet to 
retain its magnetism. 



Zinc - battery. A battery which 
decomposes zinc in an electrolyte, 
thereby producing a current. 

Zinc Currents. Negative cur- 
rents. 

Zinc - plating. The employment 
of zinc in electro-plating. 



THE END 



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